The 31 year old was found dead in a hotel room in Vancouver, Canada, just months after completing a stint in rehab to address his addiction issues, and famous faces including Rihanna, Katy Perry, Chloe Grace Moretz and Demi Lovato flocked to Twitter.com to pay their respects to Monteith.
His Glee co-stars Gwyneth Paltrow, Matthew Morrison and Kristin Chenoweth also spoke publicly about their grief, and now several other actors from the hit U.S. Tv show have broken their silence to mourn their pal.
Stamos, who appeared in four episodes of the show, has revealed he had a heart-to-heart talk with Monteith about his sobriety while they were on set together. In a post on his Twitter.com page, Stamos writes, "Heartbreaking. RIP Cory. We talked about how lucky he felt to be alive - and sober. We talked about playing drums. Glad I knew you Cory".
Mark Salling, whose character was best friends with Monteith's Finn Hudson in the series, adds, "Going through a million memories and emotions today. I'll love you always brother Cory."
Harry Shum Jr., who plays Mike Chang, laments, "At this time, please send nothing but love and light. This tragic news still doesn't seem real to me. I love you Cory", while his co-star Lauren Potter shares, "I am totally heartbroken right now. I love Cory so much this hurts my heart. Cory was always so nice to me. I have so many good memories."
Idina Menzel, who plays the onscreen mother of Monteith's co-star and real-life girlfriend Lea Michele, adds, "I hate Twitter (at a time) like this. Nothing I write will convey my sadness for Cory & all who loved him."
Jane Lynch, who turned 53 on Sunday (14Jul13), tells the New York Daily News, "It's very sad."
Other celebrities who have expressed their sadness in the aftermath of Monteith's death include new mother Jenna Dewan-Tatum, actress Patty Duke and former Gossip Girl star Kevin Zegers.
Bosses at the Gay & Lesbian Alliance Against Defamation (Glaad) have also paid tribute to Monteith, who was a longstanding supporter of the organisation.
Spokesperson Wilson Cruz states, "We mourn the loss of our friend Cory Monteith, whose support of Lgbt (lesbian, gay, bisexual, and transgender) youth and his work to end bullying served as an inspiration to countless young people. Losing such a strong ally at a young age is heartbreaking, but we are thankful for the many lives he touched through his work and advocacy. Our hearts go out to his family both at home and on the set of Glee."