NEW YORK (AP) - Facebook's latest quarterly results showed continued strength in mobile advertising, which spurred a 60 percent revenue increase in the July-September quarter. The numbers beat Wall Street's expectations for the second consecutive quarter, but after an initial after-hours trading spike, Facebook's stock took a downturn during the company's conference call with analysts. Investors may have been spooked by a remark by Facebook finance chief David Ebersman, who said the company saw a decrease in daily use among younger teenagers, an important but fickle demographic. After soaring as much as 18 percent to $57.98 after the quarterly results came out, shares of Menlo Park, Calif.-based Facebook slid to $48.44 in extended trading during the company's conference call. The stock had closed Wednesday's regular trading day down 39 cents at $49.01. The stock's fluctuations overshadowed a stellar quarter. The world's largest social network said Wednesday that it earned $425 million, or 17 cents per share, in the third quarter. That's up from a loss of $59 million, or 2 cents per share, in the same period a year ago. Adjusted earnings were $621 million, or 25 cents per share, in the latest quarter. That's 6 cents better than analysts expected. This figure excludes special items, mainly stock compensation expenses. Revenue grew 60 percent to $2.02 billion from $1.26 billion, helped by increasing mobile advertising revenue. Analysts, on average, were expecting revenue of $1.91 billion, according to FactSet. "The strong results we achieved this quarter show that we're prepared for the next phase of our company, as we work to bring the next five billion people online and into the knowledge economy," CEO Mark Zuckerberg said in a statement. Facebook's advertising revenue was $1.8 billion, up 66 percent from a year ago. Mobile ads accounted for 49 percent of the company's total ad revenue during the quarter. In the second quarter, mobile ads amounted to 41 percent of the total. The increase shows Facebook's strategy to become a "mobile-first" company is paying off. At the same time, Facebook is growing its share of the mobile advertising market. Research firm eMarketer estimates that Facebook will grab 15.8 percent of the world's mobile ad spending this year, up from 5.4 percent last year. Google Inc., meanwhile, is expected to capture 53.2 percent this year, up slightly from a 52.4 percent share in 2012. There were 1.19 billion Facebook users as of the end of September, up 18 percent from a year ago. Of these, an average of 728 million users logged in every day during the month of September, up 25 percent from a year ago. Facebook had 874 million monthly mobile users at the end of the quarter, up 45 percent year-over-year. In a conference call with analysts, though, Ebersman said that the company saw a decrease in daily use among younger teenagers. That's been a concern for some analysts who fear young people are migrating to newer sites. Luckily for Facebook, this includes the photo-sharing service it owns, Instagram. As expected, the quarter's operating expenses increased as Facebook continued to invest in growing its staff and enhancing its technical infrastructure. Total costs were $1.28 billion in the latest quarter, up 45 percent from $885 million a year ago. The company ended the quarter with nearly 5,800 employees, up 34 percent from a year earlier. Facebook went public in May 2012 at $38 per share. It took the stock more than a year to surpass that price as the company worked to prove that it could grow mobile advertising revenue at a time when an increasing number of its users were accessing it on cellphones and tablet computers. Facebook didn't start showing advertisements on its mobile applications until last spring. In the first quarter of this year, the mobile category accounted for 30 percent of total ad revenue.