Social networking looks easy as an individual. You sign-up for the service you find interesting and contribute at your leisure, in your mood, expressing your views.
For a company there much more considerations to make. In first place, you would need to define a strategy why you want to be active, how you want to do it and most importantly with whom you wish to connect. In the following video you gain some insights from Enrique Dans, professor at IE Business School and renowned blogger about technology (unfortunately in Spanish only).