The 31-year-old actor died unexpectedly Saturday in a Vancouver hotel.
Fans and fellow actors took to Twitter Saturday night to express their grief over the death of Monteith, who played Finn Hudson for six years on Glee, The Hollywood Reporter said Sunday.
Zooey Deschanel tweeted, "This is such sad news about @CoryMonteith -- what an absolutely tragic loss of a very talented young man."
Dot-Marie Jones, who has a recurring role on "Glee" tweeted, "I have no words! My heart is broken Cory was not only a hell of a friend he was one amazing man that I will hold close to my heart forever."
"I am blessed to have worked with him and love him so much! My heart is with his family and our whole Glee family! I love you all!" she added.
Kristin Chenoweth, who also appeared on the show, said, "RIP CoryMonteith. You will be loved. Always."