Mac, a popular stand-up comic and screen performer, passed away on Saturday at the age of 50 from complications due to pneumonia.
Clooney, who starred with Mac in the Ocean's series, said: "The world just got a little less funny. He will be missed dearly."
Fellow co-star Brad Pitt said: "I lament the loss of a ferociously funny and hardcore family man. My thoughts are with [wife] Rhonda and their family. Bernie Mac, you are already missed."
Samuel L. Jackson, who appeared with Mac in this year's Soul Men, described him as "one of the pre-eminent comedians of our generation", adding: "He was also an attentive husband, a great father and loving grandfather.
"I feel blessed to have shared years of friendship with Bernie Mac, and I'm honoured to have finally co-starred with him in what I consider to be his finest cinematic acting achievement."
Luke Wilson, who featured with Mac in Charlie's Angels: Full Throttle, told People: "He couldn't have been a nicer guy. He just seemed like a real family man and just a nice guy on the set. Just very kind of normal guy."