Depends on the dream, depends on the dreamer. Usually I only see a few people, at most 3 at a time, but recently I've found myself in crowds.

As for completely devoid, I can recall at most only five minutes per dream where there aren't dream characters at all. I can't remember a dream (not a fragment) totally devoid of dream characters. I've never been alone.

And then there's lucidity. I often have to seek dream characters if they are not family or close friends.