I know many stories like these. When I ask companies "Do you generate revenue via social media? Facebook, Twitter, G+ or anything?" the answer is always no. I would love to know about counterexamples if there are any.
Outside of that, well, um.... er...
EDIT: Further thought would suggest, Facebook, G+, Twitter, etc. That seems to hint that maybe the main business of social media is: spreading social media. Ruh oh.