Conan O'Brien
Followers: 2.7 million
Sample tweet: "I forgot to set my clock forward and ended up sleeping right through my clock-setting class."
After a tumultuous late-night war in early 2010, Conan O'Brien was left with dedicated fans but no network to call home. But when he started a Twitter account in February last year, everything changed. Opening with the tweet, "Today I interviewed a squirrel in my backyard and then threw to commercial. Somebody help me," O'Brien rapidly gained followers. He's used Twitter as a platform for major announcements — like his cross-country tour and move to TBS — and a way to remain in the public eye while between jobs. Now that O'Brien's show is up and running, his daily tweets keep more than 2½ million followers laughing.