I thought NSA was supposed to be limited to foreign intelligence, facebook has no such limitation. Besides IIRC CIA's IN-Q-TEL is among the first investors in facebook.
So facebook is much more that NSA, though they probably provide the NSA. AFAIK the "social media website" label is the PR/marketing way to say "global tracking/surveillance tool fueled by exploiting its registered users".
I don't know where you got this idea. The NSA is known for being close to useless in terrorism matters and champion of industrial espionage and spying on political leaders.