Depends on who is counting and for what purpose and what that person means by 'social media'...but to me, this seems like a question from a context where the answer is likely to be 'yes'.
Good luck.
Yea, probably. Posting threads and comments definitely does.
Even if you don't know the people? So, would writing comments on a 1990s geocities guestbook count, since the word hadn't been invented yet? It didn't seem "social" until all your real friends used their real names. If it's all strangers using screen names, it can't be too social.. by this definition, Twitter isn't really social media, except for the celebs using their real names.
I don't think you have to know them in person for it to count. My thinking of social media is that its more of a 2-way exchange as opposed to TV/radio/print.