eMarketer Downgrades Twitter’s 2011 Ad Revenue From $150 Million To $139.5

Twitter has been slow to expand its advertising products, which is part of the reason why eMarketer has adjusted its forecast for the company’s 2011 advertising revenue. Projected to be $150 million in January of this year, the recent report suggests that the actual 2011 ad earnings will be closer to $150 million.

But eMarketer isn’t necessarily bleak about Twitter’s future. Indeed, the digital intelligence company projects that Twitter will reach $400 million in ad revenue by 2013.