Madonna posted a video on social media of herself presenting Michael with an award in 1989, and wrote: "Another Great Artist leaves us."
Robbie Williams, whose first solo single was a cover of Michael's song Freedom, wrote: "Oh God no …I love you George …Rest In Peace x".
Boy George wrote: "He was so loved and I hope he knew it because the sadness today is beyond words. Devastating.
"What a beautiful voice he had and his music will live on as a testament to his talent. I can't believe he is gone. I hope the Buddha will hold him in his arms."
South Central Ambulance Service were called to Michael's property at 13:42 GMT on Christmas Day. Thames Valley Police also attended and Michael was confirmed dead at the scene.
They added: "At this stage the death is being treated as unexplained but not suspicious. A post-mortem will be undertaken in due course. "
A small heart wreath and a rose are among the tributes left outside the front door of Michael's Goring home, a detached property by the River Thames.
