There are numerous articles, books, conferences and training program to help you define your social architecture, and I do not have the ambition to explain you the right way to do it (at least not in this article), but if you are looking for more explanations and advices, youshouldread the original post here: Social Media Landscape 2012.
The whole lot is slated to ship out right about now, and if you're craving more in-depth details on any one in particular, the read links below should do the trick.