SAN FRANCISCO - Facebook Inc doubled its mobile advertising revenue in the fourth quarter, a sign that the No.1 social network is seeing early success in expanding onto handheld devices as more of its users migrate to smartphones and tablets. Investors want to see evidence that CEO Mark Zuckerberg 's 8-year-old company is delivering on promises to develop a full-fledged mobile advertising business, a challenge facing many of today's technology leaders including Google Inc . But the growth trailed some of Wall Street's most aggressive estimates. Shares of Facebook were down roughly 3 percent at $30.21 in after-hours trading on Wednesday, regaining ground after falling more than 8 percent immediately after the numbers were released. Mobile revenue estimates among some analysts and investors were unreasonably high, said Sterne, Agee & Leach analyst Arvind Bhatia. "As a result the stock was set up f...