Well Retroshare somewhat falls into this category. It is not Coin-Based however, rather related to Bittorrent DHT technology und not well documented.
There is also the Bitmessage protocol which uses Coin technology for exchanging mail.
I do not know why you would build such a system as a Coin network, plain BT style DHT is more suitable for this purpose in my opinion. I do not know any good reason why Bitmessage does it this way either. I think it is just overcomplicated and not well thought through. The usecase is just very different from Bitcoin.
I mean, what would be the purpose of the block chain? Prevent double friending?