Shaquille O'Neal announced his retirement via a Twitter video. And potentially millions watched the 18-year basketball veteran announce his departure from the league that made him famous.

Still, only 13 percent of online adults use Twitter, according to a new report from Pew Research Center. That, the researchers said, represents a significant increase from the eight percent of online adults who identified themselves as Twitter users in November 2010.

What's more, 95 percent of Twitter users own a mobile phone, and half of them access the service on their handheld device, according to the study.