Katharine McPhee, who duetted with Spence during his time on season 19 of the show, shared clips to her Instagram story of them together.
"I received very tragic news tonight ... Sweet @williespenceofficial passed away in a car accident. Only 23 years old. Life is so unfair and nothing is ever promised.
"God rest your soul Willie. It was a pleasure to sing with you and to know you."
McPhee also reposted the last video Spence shared of himself singing a Christian song in a car right before the accident happened.
"He posted this right before the accident," she added.
Followers and fans of Spence and the show have shared their tributes online.
"Fly and sing with the angels and dance among the stars friend! RIH️," commented one.
"OMG I am so at a loss for words. Not you Willie! Wow … ️ Rest in Paradise, king," commented another.
Film producer Randall Emmett also paid tribute to the star on his Instagram story.
"My heart is broken and my prayers go out to his family," he wrote.
"I was lucky to have him sing for me live at my home and other events, I will miss you my friend. I know you touched so many of us. I'm heart broken."
During the season 19 finale last year, Spence sang Georgia on My Mind, A Change Is Gonna Come and Stand Up. The judges were moved by his performance, but he ultimately received fewer votes than Chace Beckham, who won the title of American Idol.