"Social media" is considered to be a noun to define that type of site/community/service/etc. and can therefore be used in singular. The title is worded as "Is <concept> ..." rather than "are all the things that make up <concept>...".
No. That's grammatically incorrect. The word media is plural regardless of whether or not you're using it to describe a general concept. Consider another example. You wouldn't write "Is People Useless."
