In the case of reddit I heard, that - at least in the very early stages, the creators themselves provived a lot of the content, and even hired some people almost exclusively for that purpose. I can't remember where I read it though.
Part of the Udemy course Huffman was offering he said this [1] And honestly, it doesn't bother me all that much. I see it like an engine needing a big spray of gasoline and a spark before it can run. Just because it didn't start with pistons running doesn't mean it's a bad engine. I see it more as faking it till they made it, and it worked. They were their own biggest fans.
Yeah, they had a post form that had a field for username that was available only to the founders. So they could post content and then invent a username to make it appear that there were lots of unique users. They discuss it in this podcast. http://one.npr.org/?sharedMediaId=545635014:547386946
