Twitter is now used by 13 per cent of US adults on-line, up from 8 per cent in November, as more older Americans embrace the service. Among Twitter users who own mobiles, 54 per cent have used the mobile devices to access the social media service, according to a report by the Pew Research Center. Twitter use has more than doubled since late 2010 among people ages 25 to 34, to 19 percent, and increased among adults ages 35 to 44, to 14 per cent. Usage for those ages 55 to 64 doubled to 8 per cent. \"It\'s more in the public consciousness than it was probably six months ago,\" Aaron Smith, an analyst with Pew in Washington, said. \"Older people are kind of jumping in, taking a look at what\'s going on. In general, it seems that Twitter is less confusing, for lack of a better word, than it was, say, this time last year.\" Twitter, competing with Facebook, is trying to improve its products amid management changes designed to attract more users and advertisers. In March, co-founder Jack Dorsey, who stepped down as CEO in 2008, became executive chairman and head of product development. Dick Costolo, who helped introduce a new advertising service for companies on Twitter last year, became CEO in October, replacing co-founder Evan Williams. \"We\'re growing like a weed,\" Costolo said at AllThingsD\'s D9 Conference in Rancho Palos Verdes, California. \"The beauty of Twitter is that more and more people are flocking to it because it\'s shrinking their world.\" The Pew report\'s estimates of users was conservative, Costolo said, noting outside researchers fail to accurately track Twitter usage. Still, he declined to give specific active user numbers. Twitter\'s website is no longer where the \"vast majority\" of users reside, he said. There has been dramatic growth with Twitter for mobile devices, including Apple iPhone. To woo more users, Twitter recently unveiled a service that will enable people to more easily share photos, the company said on its blog. The social network also is updating its search service that aims to give more relevant posts and show related photos and videos. As for advertisers, Twitter has 600 to 650, up from 150 in 2010, Costolo said. Advertisers, more than 80 per cent of whom return to the site, have run more than 6,000 campaigns. Ad sales on Twitter may more than triple to about $150 million this year, according to EMarketer Inc. Facebook brought in ad revenue of $1.86 billion last year, EMarketer estimates. Twitter still trails overall social networking adoption, including Facebook, at about 65 per cent, Pew\'s Smith said. From / Gulf news