6. Britney Spears
Twitter handle: @britneyspears
Joined Twitter: Sept. 22, 2008
Followers: 21,614,348
First tweet: Oct. 10, 2008. "Welcome to Britney Spears' Twitter! Follow the latest in Britney news and get updates straight from Britney and her entourage."

Note how Swift gives fans a little glimpse into her life with her first post while Spears keeps them at arm's length behind several layers of security. This is what a decade of pop stardom, paparazzi stalkers, publicized breakdowns and breakups and parenthood can do to a person. Get ready, Taylor.

Britney's released two albums since -- with 2008's Circus going platinum and last year's Femme Fatale selling 1 million copies in the U.S. -- and has had three No. 1 singles with Womanizer, 3 and Hold It Against Me. Like her fellow blonde 2000s Disney pop contemporary Christina Aguilera, though, Spears has settled in to life as a talent judge. Fox's X Factor seems to agree with her and her Twitter numbers, even if her life isn't quite the tabloid fodder it was five years ago.

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