Update: Tag no longer exists.
Tag social-networks was in use for ~40 Open Qs. It showed 13 followers and a Usage guide of:
On Web Applications, the tag 'social networks' refers to a website where users keep in communication with others and share information. Examples include Facebook, Twitter, Google+, Diaspora*, and others.
Do we need it?
Frankly, I don't think we need any. Questions about social networking or social networks in general is almost certainly going to be too broad. Social medcia is even broader. Otherwise, you need to add a separate tag to identify the social network you're asking about, making the social network(s|ing) tag superfluous.
If one of them survive, the others should be made synonyms.
