Some Internet users make the claim that Facebook is recently becoming very overpopulated.
To deem something overpopulated is to insinuate that the additional users somehow lessen the experience for the existing members in one way or another.
There is no physical meeting place for members of the site, so the term overpopulated cannot be applied to a lack of space.
While it may be true that there is indeed a steady increase in the Facebook population, it is difficult to declare the site overpopulated.
These are the users who make the claim that Facebook is recently becoming very overpopulated.