A social network is a natural monopoly due to the network effect. It wouldn't make any sense to split it up. Regulating it like any other natural monopoly could make sense.

Amazon is certainly not an online shopping monopoly. It's just a superior service. I can get a similar online shopping experience from Wal Mart and many others. If Amazon can offer us such good service through having its own big network of warehouses, drivers, etc. that's impossible with a bunch of smaller companies then I say let them be as big as they are so long as they don't egregiously abuse it.