Facebook's stock is flying high after the world's biggest social network posted higher revenue from mobile ads and delivered a healthy second-quarter profit that reversed a loss a year earlier.

Facebook Inc. said Wednesday that it earned $333 million, or 13 cents per share, in the April-June period. That's up from a loss of $157 million, or 8 cents per share, a year ago. Adjusted earnings were $488 million, or 19 cents per share, above the 14 cents that analysts were expecting.

The Menlo Park, California-based company's stock jumped $4.93, or 18.6 percent, to $31.44 in extended trading after closing at $26.51. The stock priced at $38 when Facebook went public in May 2012 and hasn't hit that since.

"I'm completely surprised," said Gartner analyst Brian Blau, summing up the sentiments of many investors who've watched Facebook's stock price stagnate over the past year.

"I was actually thinking that maybe they would have a soft quarter," he added, citing a softening of advertising revenue _ Facebook's bread and butter _ across the industry. "That seems not to be the case."

Facebook's revenue grew 53 percent to $1.81 billion from $1.18 billion, well above the $1.62 million that analysts polled by FactSet were expecting. Facebook has also quickened the pace of its revenue growth. In the first quarter, revenue grew 38 percent and in the fourth quarter of last year, 40 percent.

Mobile revenue was $655.6 million, or 41 percent of the quarter's total advertising revenue of $1.6 billion.

"We've made good progress growing our community, deepening engagement and delivering strong financial results, especially on mobile," said CEO Mark Zuckerberg, in a statement. "The work we've done to make mobile the best Facebook experience is showing good results and provides us with a solid foundation for the future."

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

That said, Google is a distant No. 1 when it comes to mobile ads. EMarketer estimates that the company held 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.

Facebook has also been working on growing its international advertising revenue, since most of its users live outside of the United States. The company announced this week that more than 100 million people access Facebook using traditional, non-smart phones in countries like India, Indonesia and the Philippines.

Facebook had 1.15 billion monthly active users as of June 30, up 21 percent from a year ago. The number of monthly mobile users grew 51 percent to 819 million.