More adult Internet users (13%) are using Twitter as of end May this year than was the case back in November 2010, when 8% were using it, according to the Pew Research Center’s internet & American Life Project. Asking participants how they accessed Twitter for the first time, Pew project researchers found that more than half (54%) do so via cellphone.

Young adults 18-29 continue to make up the single largest part of Twitter’s user base (18%) but the service has made strong gains with online adults 30-49, 14% of whom use the micro-blogging service, more than double the number reported in the November survey. Growth was also particularly strong among those 25-34: it more than doubled, from 9% to 19%. Also contributing to the pick-up, the percentage of online adults 35-44 accessing Twitter increased to 14% as of May from 8% in November.

African-Americans and Latinos tend to use Twitter more than whites. The gap between online African-American and online white adult Twitter users increased to 16% (25% vs. 9%) between November 2010 and May 2011. More than 10% on online African-American adults access Twitter on any given day, double the rate of their Latino, and 4x the rate of their white counterparts. 19% of online Hispanic adults used Twitter per the November survey results, 5% on any given day.