I saw this on a miniature scale when I created a new subreddit ( http://reddit.com/r/LSAT ) I spent about two weeks creating quality articles for the sidebar, personally replying to every submission/comment, manually recruiting anyone who mentioned the LSAT, and reaching out to moderators of related subreddits for links. Mercifully, a subreddit is a small thing to launch, and after two weeks the place became self-sus…
Their attitude (having tried it) is now if the community doesn't build itself it won't sustain itself. If you've got a working community then you can promote it but this sort of work won't work to build a community that's not already there.
Not saying that what PG says isn't true for start-ups which are obviously different, but it may be relevant in your case.