For more on this study, including who's most at risk, just keep reading.
Some criticize the study, saying that it's not a clear conclusion that the to things are related, but one of the lead researchers defends the findings, saying:
"It does make sense that these technologies make it easier for kids to fall into a trap of working too hard to fit in. If they’re working that hard to fit in through their social networks, they’re also trying to fit in through other behaviors they perceive as popular, like smoking cigarettes or drinking alcohol, having sex and getting involved in higher-risk adolescent behaviors."
Girls, minorities, and those who come from female-headed households are deemed most at risk; the study also found that the most at-risk teens also described their parents as "lenient," prompting the authors to recommend more parental involvement and monitoring of teens' use of the sites.