Ethereum is building out a p2p messaging system called Whisper: https://github.com/ethereum/wiki/wiki/Whisper

This doesn't use the ether gas as payment, but a PoW to encrypt the message locally then sent.

Ethereum's data store will come from Swarm: https://github.com/ethersphere/swarm

With these two additional pieces it is trivial to build and conduct a social network on ethereum's blockchain.