Facebook's stock passed $38 for the first time

Shares of Facebook stock increased 1.2 percent to $38.08 on Wednesday.

Facebook's stock has passed its $38 IPO price for the first time since its rocky public debut last May, crossing a symbolic hurdle that has eluded it for more than a year.

Shares of Facebook Inc. increased 1.2 percent to $38.08 in morning trading Wednesday. That's the highest the stock has traded since the company's highly anticipated initial public offering ended with a thud. The stock is up by more than 50 percent since last week.

The world's biggest online social network has been on a roll since reporting stronger-than-expected earnings on July 24. Investors are especially upbeat about its fast-growing mobile advertising revenue.

Facebook's ability to grow mobile revenue was one of the biggest concerns in the weeks leading up to its IPO last year. Investors were worried that its ad business was not migrating to mobile gadgets as quickly as its user base. Facebook urged patience.

In the April-June quarter, Facebook derived 41 percent of its ad revenue from mobile advertising, or about $656 million of $1.6 billion. That's up from zero in the spring of 2012 and from 30 percent in the January-March quarter of this year. CEO Mark Zuckerberg said last week that the company has "made good progress growing our community, deepening engagement and delivering strong financial results, especially on mobile."

Still, Facebook has room to grow. Research firm eMarketer expects Facebook to increase its mobile advertising revenue more than fourfold to more than $2 billion this year. This would give the Menlo Park, Calif., company a 13 percent share of the global mobile ad market, up from about 5 percent last year.

Facebook is currently No. 2 in mobile ads, well behind Google. EMarketer estimates that Google had a 52 percent share of the global $8.8 billion mobile ad market last year. This year, the firm expects Google's share to grow to 56 percent.