U.S. microblogging platform Twitter on Friday marked its fifth anniversary since public debut. \"Twitter, then called Twttr, opened to the public five years ago today,\" the company said in a Tweet, a short message within 140 characters users are allowed to communicate on the website. \"Twttr is a new mobile service that helps groups of friends bounce random thoughts around with SMS,\" co-founder Biz Stone described the service in a blog post on July 13, 2006, two days before its public debut. \"There were 224 Tweets sent on July 15, 2006. Today, users send that many Tweets in less than a tenth of a second,\" said the San Francisco-based company. Twitter said more than 600,000 new users signed up on Thursday while it took it more than 16 months to reach the first 600,000 Twitter accounts. The tipping point for the service\'s popularity was the 2007 South by Southwest festival, a set of film, interactive and music festivals and conferences that take place every March in Austin, Texas. During the event, the Tweets sent per day grew from 20,000 to 60,000. With an estimated user base of 200 million worldwide, some 200 million Tweets are generated and 1.6 billion search queries are handled every day, the company said. According to research firm EMarketer, advertising sales on Twitter is expected to reach 150 million U.S. dollars this year. SharesPost, a secondary market for privately held companies, has assessed Twitter\'s current worth at 6.8 billion dollars.