Ask HN: Books/Articles on Social Networking and Game Theory

I'm interested in reading more about the psychology of social networking, particularly in regards to how they might relate to rewards and game theory.

Anything to do with examples of how businesses are using game related rewards such as points, levels, and achievements to reward user interaction with the site and build communities centered around a service or a product.

I know they exist, but it's hard to find elements that combine the two.

Thanks