The engaged couple appealed for funds and helped answer phones at the event that was staged at the Shrine Auditorium in Los Angeles.
Gwyneth Paltrow reunited with her Country Strong costar Tim McGraw.
Julia Roberts couldn't wait to pose for the picture with gold medal gymnast Gabby Douglas.
Alicia Keys, Coldplay and Taylor Swift all performed.
Robert Pattinson chipped in, the night after he was a presenter at the MTV Video Music Awards.
Cancer "picked a fight with the wrong guy," said Michael Douglas, who had throat cancer. "Cancer didn't bring me to my knees, it brought me to my feet. I stand tonight because I want to be part of this effort to find an end to cancer. This is possible."
Bikini Babe Taylor Is Swiftly Becoming A Kennedy