The post-market rally in Facebook shares collapsed like a souffle after the company made the disclosure in a conference call with analysts. The stock price was up about 15% after it released strong Q3 earnings. But the price is now virtually flat after CFO David Ebersam said the company had seen a drop in use among young teens. “Our best analysis on youth engagement in the U.S. reveals that usage of Facebook among U.S. teens overall was stable from Q2 to Q3, but we did see a decrease in daily users, specially among younger teens.” Although he considers the data of “questionable statistical significance,” he added that he “wanted to share this with you now since we get a lot of questions about teens.” Indeed, early this month investment firm Piper Jaffray said in its “Taking Stock With Teens” survey that “the popularity of Facebook is waning among teens, with 23% citing it as the most important [social media platform], down from 33% six months ago and 42% a year ago.” That seemed to contradict CEO Mark Zuckerberg‘s comment to analysts in July that while “there has been a lot of speculation reporting that fewer teens are using Facebook,” company data showed that it “just isn’t true. … We believe that we’re close to fully penetrated in the U.S. teen demographic for a while and the number of teens using Facebook on both a daily and monthly basis has been steady over the past year and half.”

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