Geoff Cook, co-founder and CEO of myYearbook.com , performed some research to learn why teens aren’t using Twitter. Here’s one result. The New York Times has claimed that 11 percent of Twitter consists of teenagers. “The implication is that 11 is a small number, but if we look deeper, it turns out that Twitter has a higher concentration of teens than Facebook,” he wrote for TechCrunch . Facebook is only 9 percent teen.