I have four, in two pairs. Two of them are tied to my real name--adult books and kid books. Two of them are tied together but unrelated to me -- erotica and controversial topics.
All four have their own site or blog. I have no FB author pages. I don't see a real use. But I do have two twitter accounts, one for each name pair. Each says "also writing as X."
I find I go in cycles on my names, so it's not as bad as it might seem. I spend a few months as one, then a few months as the other. Only two of the names have a good seller among them, but I'm about to go whole-hog on a third name to get it going, and the fourth name is about to head to agents and trads.