Serious Business, the developer of the “Sell Your Friends” app on Facebook, has raised a $4 million first round from Lightspeed Ventures. The popular app claims over 600,000 daily active users, although, just on a personal note, if you invite me to play, I will block you for good. This adds the company to the growing list of social app developrs to have raised money including Slide and RockYou (the big ones) as well as Zynga, which is more focused on Games. Here’s how MediaPost describes the app: “The game lets people buy and sell friends like commodities with virtual currency. When someone buys you, your value increases.” Co-founder Siqi Chen told AllFacebook that the raise valued in the “healthy double-digits” (million), although that leaves open a big range.