SAN FRANCISCO (AFP) - Twitter on Tuesday broadened its reach by letting websites add Follow buttons that visitors can click to begin tracking posts at the globally popular microblogging service. Twitter billed the button as a new way to follow Twitter accounts directly from the websites you visit every day. The feature was rolled out the same day Web advertising company AdGrok announced it has been bought by San Francisco-based Twitter. When Twitter approached us and asked if wed be interested in working on their monetization platform, we realized that this was a once-in-a-lifetime opportunity that we just couldnt pass up, AdGroksaid in a blog post. Starting today, we will be working full-time on Twitters revenue engineering team. Websites that took part in the Follow button launch included online venues for pop stars Lady Gaga, Justin Bieber and Britney Spears as well as news, sports, and videos. More than 50 sites have added the Follow Button as part of todays launch, making it easy for people to discover the Twitter accounts of their favorite reporters, athletes, celebrities, and other personalities, Twitter said. Twitter took in $45 million in global advertising revenue in 2010 and was on track to more than triple that figure this year, according to industry tracker eMarketer. Approximately 20.6 million people in the United States will use Twitter at least once a month this year in a 26 percent increase from activity seen at the microblogging service in 2010, eMarketer reported.