Stars React to Michelle Trachtenberg's Death: Sarah Michelle Gellar, Rosie O'Donnell, Blake Lively & More

Not long after Trachtenberg's shocking passing was confirmed, fellow celebrities and former co-stars began paying tribute to the late actress.

Sarah Michelle Gellar, who played Trachtenberg's older sister on Buffy the Vampire Slayer, shared her tribute on Thursday morning. Alongside photos of the two from the show and together in real life in the years since, she wrote, "“Michelle, listen to me. Listen. I love you. I will always love you. The hardest thing in this world, is to live in it. I will be brave. I will live… for you”
💔💔💔🗝️"

The quote references something Buffy told Michelle's character, Dawn, before sacrificing herself to save her sister in the Season 5 finale, "The Gift." The tribute also include a photo of Gellar and Trachtenberg with Shannen Doherty, who died from cancer in 2024.

Trachtenberg's Buffy the Vampire Slayer co-star, Alyson Hannigan took to Instagram to share how "deeply saddened" she is to hear the news of Trachtenberg's passing. Hannigan recalled her bringing a "loving energy to the set of Buffy."

David Boreanaz took to his Instagram Story to remember Trachtenberg, writing, "So very sad... horrible news. RIP and prayers to her and her family.

Fellow Buffy co-star James Marsters, who played Spike, shared a tribute as well -- writing, "My heart is heavy today. We have lost a beautiful soul. Michelle was fiercely intelligent, howlingly funny, and a very talented person. She died much too young, and leaves behind scores of people who knew and loved her."

"My heart goes out to her family who are good people, and are suffering the greatest loss anyone could bear," he continued. "I hope everyone can give them space to heal in this most difficult time. Godspeed Michelle. You are missed."

Buffy alum, Emma Caulfield shared a photo of the pair together on her Instagram Story captioning it: "I'm so sorry your bright light died so young. Our Buffy family lost a sister today... Rest in peace lovely Mish Mish. You were loved."

While acknowledging she wasn't as close to Michelle as her other Buffy costars, Charisma Carpenter said "it is never easy to see someone so young, bright, beautiful, and full of promise pass away. It's devastating, actually."

"I extend my deepest condolences to those who knew her better than I did -- those who had the pleasure of working with her, those who loved her with all their might, her family, and her partner, whom I never met. I’m so sorry for your loss," she continued. "I would be remiss not to acknowledge the undeniable impact she has had on the lives of her fans worldwide. She will live on through her performances and her love of storytelling forever. Rest easy, Michelle. 🕊️"

Blake Lively, who starred in Gossip Girl alongside the late TV and film star, sharing a photo of them film their first day working together to Instagram and saying, "She was electricity."

"Everything she did, she did 200%. She laughed the fullest at someone's joke, she faced authority head on when she felt something was wrong, she cared deeply about her work, she was proud to be a part of this community and industry as painful as it could be sometimes," she continued, before sharing, "Time passes. You take for granted that you get the chance to see an old friend."

"The real tragedies in life are the ones that blindside you on an idle Tuesday," said Lively, telling others to hold their loved ones close.

Fellow GG star Taylor Momsen also shared a lengthy tribute, writing, "In shock…When I met this girl 17 years ago I knew we'd be friends..she was smart and sassy, bold and sensitive, funny as f--k and filled with fire. She was simply awesome,"

"I'll miss our late night calls that no one should ever hear but us. She was always in my corner and there to support me whether I was right or wrong. I will miss you everyday my love ... I think we truly understood each other and I am so grateful to have had a friend like you in my life for so long," she continued.

"You were a true friend to me which is a rarity in this world and I can't believe I won’t hear your voice again ... I hope you're f--king up heaven for both of us ... I love you so much Michelle, my heart is on the floor," she concluded. "I'm still in shock but I needed to honor her, she deserves more than this. I grieve with all her fans around the world, and my heart is with her family and loved ones. I have so much to say, but she’s the only one I’d want to say it to, my love to you all xxt

Chace Crawford also shared an Instagram tribute, writing, "Michelle was one of a kind. I remember her coming on set for the first time and just absolutely owning it. She was a force of nature and just so so unapologetically funny and magnetic.. remembering those years with a big smile. Just a terrible loss. Love you ❤️"

Ed Westwick wrote, "So sad to hear of the passing of @michelletrachtenberg. Sending prayers."

GG alum Jessica Szohr added, "This amazing woman bursts onto the scene with energy that instantly brings a smile to your face. She's not only a true professional, but she's also the perfect antidote to anyone who takes life a bit too seriously."

Her tribute continued, "Her kindness and outrageous sense of humor create an atmosphere of joy, both on set and beyond. We shared countless laughs during filming, over the phone, and at various events. Her captivating stories are so entertaining that you can’t help but want to hear more! She’s truly one of a kind. 💔"

Rosie O'Donnell -- who starred alongside Trachtenberg in 1996's Harriet the Spy, which was released when Trachtenberg was just 10 years old and marked her big-screen acting debut -- called the news "heartbreaking."

"I loved her very much. She struggled the last few years. I wish I could have helped," O'Donnell said in a statement to PEOPLE.

In a followup post to Instagram, she added, "god i loved this little person - my harriet - michelle t … 🫶🏽🤟🏽❤️🙏🏾 so much love to her amazing mom lana and her sister - both loved her endlessly #gone2soon"

Kim Cattrall, who played Trachtenberg's coach in Disney's 2005 film, Ice Princess, also paid tribute to the 39-year-old TV and film star, sharing a photo of the pair form the film on Instagram, writing, "Rest in peace sweet Michelle 💔."

Longtime friend Lydia Hearst shared a lengthy tribute as well, saying that it's been "extraordinarily difficult to muster the strength and find the words for this."

"I don’t even know how to begin to process the fact that you are gone ...  Thirty years of friendship. You were my best friend, the single person who knew me better than anyone else, my chosen family," she wrote. "I have been trying to wrap my head around this monumental loss ... My soul hurts. I am heartbroken. Nothing could have ever truly prepared me for this moment."

"Our friendship was deep and powerful; you were my soul sister and soulmate, the honorary auntie to my daughter, my closest friend in life," she continued. "We loved one another unconditionally through all stages and ages of life, never judged, and were always there. All of my life's greatest milestone moments include you. We knew one another better than anyone else. Your endless wit, energy, sass, and love are unparalleled."

She concluded her post: "We always laughed and planned on how we were supposed to grow old and eccentric together. Unfortunately, fate had other plans. Through all of life’s ups and downs we were each other’s constant. We were bonded for life, and now that bond is broken, and so am I. Life without you will never be the same. I love you Michelle, always and forever."

Melissa Gilbert penned a heartbreaking message for Trachtenberg following the news, sharing a photo from their 1996 film, A Holiday for Love, writing, "Oh Michy … and we lived so close to one another."

She continued, "My heart aches for your family and all those who loved you so."

Glee star Chris Colfer shared how "lucky" he felt to be Trachtenberg's friend.

"Michelle was the absolute sweetest and one of the most supportive people I knew," he wrote on his Instagram.

Her death was first reported by the New York Post, citing police sources, with those sources telling the news outlet her death is not being investigated as suspicious.

According to TMZ, she recently underwent a liver transplant and police believe she died of natural causes. Per the outlet, police and paramedics responded to a call for a woman in cardiac arrest, and found Michelle unresponsive. She was pronounced dead on the scene.

Perhaps best known to film and television audiences for her work in Gossip Girl, Buffy the Vampire Slayer, and Harriet the Spy, Trachtenberg has largely remained out of the public eye since 2023, but was still active on social media, sharing selfies as recently as two weeks ago.

More celebrity tributes to Trachtenberg continued to roll in Wednesday, including from her fellow Nickelodeon alum, Kenan Thompson, ex Shawn Ashmore and more.

See their moving messages to the late actress below: