Twitter is increasingly focused on the bottom line. That’s why the microblogging service is rolling out new ad formats, such as Promoted Tweets in Timelines, which enables a marketer to pay to target a consumer with a tweet based on his location, demographics or interests, and making acquisitions that could pave the way for a self-service ad format. All of Twitter’s existing ad formats require marketers to work with a member of Twitter’s sales team.

Those efforts may help Twitter’s revenue reach $259.9 million this year, an 86.3% jump from $139.5 million in 2011, according to a forecast released today from research firm eMarketer.

The forecast says that Twitter’s revenue will continue to increase over in the next two years, but at a slower pace. EMarketer says that Twitter’s revenue will reach $399.5 million in 2013, a 53.7% jump from 2012, and $540.0 million in 2014, a 35.2% increase from 2013.

90% of Twitter’s revenues come from U.S.-based advertisers, says eMarketer. Marketers from other countries contributed just $26 million to the microblogging service’s ad revenues in 2011. But that will likely begin to change in the next few years, says the report, even though it suggests that 83% of dollars will still come from the U.S. marketers in 2014.

Despite its strong growth, Twitter’s revenue represented only about 5% of the estimated $2.74 billion marketers spent on social marketing last year, according to eMarketer. Facebook attracts most of the social marketing spend. U.S. marketers spent roughly $2.01 billion on Facebook ads in 2011, up 66.1% from $1.21 billion a year earlier.