18. Ben Silbermann & Kevin Systrom (Tie)
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Silbermann (left) and Systrom (right)

Ben Silbermann
Age: 30
Co-founder and CEO, Pinterest

The CEO of the fastest-growing website in Internet history may not be a coding genius, but 19 million visit his image-sharing site every month. Silbermann is a collector with a strong design sense. But the Des Moines native knows what he likes, and it happens to be liked by a lot of other people too: It regularly beats out Twitter and Facebook in driving traffic to smaller websites. And its growth shows no sign of slowing. Pinterest added apps for the iPhone, iPad, and Android this summer, and switched to an open-registration process. (Previously users had to be invited to join.) In September, Silbermann took on a role even bigger than running a company valued at $1.5 billion. He became a father.

Collect this: Silbermann never lost his childhood love for stamp collecting (but he did give up on insects and rocks).

--Ryan Bradley

Kevin Systrom
Age: 28
Co-founder and CEO, Instagram

Instagrammers, rejoice! You were indeed on to something when you came in droves to the new photo app two years ago. So were we: Systrom, No. 39 on last year's list, this year sold his baby to Facebook for $1 billion (because $1 million isn't cool). Systrom says the 16-person Instagram team is still independent within Facebook, and in 2013 will expand. Indeed, Systrom isn't going anywhere: "Other people sell and check out," he says, "but we have no interest in doing that. When the founders leave, that's when the soul of a company goes away."

Mobilize: Word has it that Systrom will be a key player in beefing up Facebook's mobile presence.

--D.R.


  @FortuneMagazine - Last updated October 17 2012 05:11 PM ET
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