StumbleUpon ^[1], the personalized discovery engine has hit a serious growth spurt. In the past 16 months, the company has doubled its user base to 20 million people who “stumble upon” interesting web pages that the site has selected. StumbleUpon is now said to drive more traffic to websites than Facebook.

Although it has experienced tremendous growth, StumbleUpon still suffers from a visibility issue. But that will soon change. The company already launched iPhone, iPad and Android apps in 2010; and although it’s user base is not exactly in the neighborhood of, say, Tumblr (31 million blogs) or Twitter (200 million registered users), a $17 million funding infusion, which fueled a hiring spree, has helped the company ramp up growth. What’s next for the StumbleUpon? International expansion, says CEO Garrett Camp.

Read more at Mashable ^[2].