NEW YORK: The number of Americans using the microblogging website Twitter could reach 18.1 million in 2010, compared with just 6 million last year, eMarketer has predicted.

While marketers and brands have been keen to increase their presence on social networking portals, such a strategy can prove risky, and Biz Stone, co-founder of Twitter, has also argued traditional advertising is not a "good model" for the website.

eMarketer estimates that some 3.8% of the US population used Twitter last year, a penetration rate that will rise to 7.4%, or 12.1 million, this year, and to 18.1 million in 2010.

The company argues these consumers will access the social media service at least once a month, either via its main portal, their mobile phone or through an application stored on their computer desktops.

Data sourced from AdWeek; additional content by WARC staff