Demand side advertising platform Triggit, which is among a limited group of companies with access to the Facebook Exchange, today announced it raised $7.4 million in a Series B round led existing investors Spark Capital and Foundry Group.

Triggit was one of the original eight DSPs involved in the beta of Facebook Exchange, an advertising system that allows third-party platforms to place retargeting ads on the social network after users visit external websites marked with cookies. Now there are about 20 FBX providers. The exchange is one of the most buzzed about features Facebook introduced this year, and early partners are reporting lower costs per acquisition and other benefits over other exchanges.

Triggit says with FBX it has seen one-fifth the CPA and four times the ROI compared to traditional campaigns. The company also says Facebook users are clicking and converting throughout the day, whereas other exchanges tend to skew toward post-work hours.

Besides FBX, Triggit enables real-time bidding on nine other major exchanges including Google, Pubmatic, Admeld and Rubicon across several platforms, including mobile and video opportunities. The San Francisco-based company raised $4.2 million in 2010, and has since opened offices in Boston, New York City and Los Angeles. Triggit says this quarter its team has grown 50 percent, with one-third of the hires joining the engineering department. Triggit’s clients include Hilton, Kmart and Lowes.