Monteith was found dead in his hotel room in Canada on 13 July (13) after a drink and drugs binge, and his passing was on Rivera's mind as she attended the 2013 Giffoni Film Festival.
The actress held a question and answer session with fans at the event, but she called for a moment of silence to pay tribute to her friend.
She then sombrely declared to the crowd, "Thank you all."
Rivera had previously spoken out to mourn her pal after news of the tragedy broke, stating, "The entire Glee family and I are deeply saddened by this tragedy. Cory was and always will be a part of my own family and a good friend. He was a special part of this world and will forever be missed."