On Thursday evening, following the second day of searching by authorities in Ventura County, Lovato -- who played a love interest for Rivera's Santana Lopez on "Glee" -- shared a rare tweet asking her followers to pray for the actress' safe return.
"I don't tweet often but sometimes my tweets come true so, together let’s manifest on twitter that Naya will be found safe and sound!!" she wrote.
On Friday morning, fellow "Glee" costar Iqbal Theba -- who played Principal Figgins -- echoed Morris' sentiments.
"I want to Thank 100+ Volunteers, Police & everyone who are helping in Naya's recovery efforts," he tweeted. "Please, keep looking for her. Bring her home, please."
The Ventura County Sheriff's Department began a rescue mission for Rivera on Wednesday, after her son Josey was found asleep and alone on a pontoon boat in Lake Piru. On Thursday, that mission was shifted to a "recovery operation," as Rivera was presumed dead.
During a press conference, they said there were "no sights of foul play" and said her disappearance appeared to be "a tragic accident."
They added that their goal was to bring "Ms. Rivera home to her family so that they can have closure."