Ask HN: Growth of my service is stagnant. What next?

I run web site http://www.fbchatroulette.net/ (Facebook Chatroulette) and, amazingly, service has more than 1300 Facebook fans and about 15000 registered users. But growth is stagnant - no hockey stick.

I wonder what can I do to scale up this service. Is there some low hanging fruits I'm forgetting? Is it that I need to improve user interface? To make it as dating site? To add different games? Maybe to add offline random chat?