Backyard Monsters developer Kixeye announced a third round of funding today totally $18 million from Jafco Ventures, Trinity Ventures and Lightspeed Venture Partner. Additionally, Zynga co-founder Andrew Trader will join the developer’s board.

Back in April, the company formerly known as Casual Collective re-branded as Kixeye and focused all development on the Facebook platform. Since that time, the developer has launched Battle Pirates and is set to bring out a third Facebook-only game, War Commander, later this summer. The total employee headcount of the developer has gone from 3 to 60 in the last 18 months and our AppData traffic tracking service puts its overall growth in monthly active users up 41% to 5.1 million and its daily active users up 37% to 1.1 million since the start of 2011.

The key to Kixeye’s success appears to be targeting a niche “hardcore” market in a manner similar to Kingdoms of Camelot developer Kabam. These focused approaches appear to be paying off; Kixeye claims that Battle Pirates players spend 20 times the industry average. Even with revenues like that, however, the developer has had raise some capital to become completely profitable, netting $4.5 million in funding prior to this round.