A medium is nothing more than a material used to convey ideas. Paint and canvas are a medium. Video is a medium. Words are a medium, whether displayed on paper or a screen.
So this is absolutely a social medium. (It's only one, so the singular medium would be more appropriate than the plural media, I suppose.)
@EverydayMoggie Interesting! Your interpretation of what "social media" is referring to is quite different from mine. I thought the "media" was the multimedia content shared along the social network, and that's also why it is plural.
In either case of the interpretation of the noun, what would you say the verb is? What do we do here?