In our personal experience, for the PRE-ICO of Experimental (https://e11.io) we rely a lot on forums and reddit. Also facebook and twitter, but not that much.

We don't have any bounty program going on, we are not willing to give away our tokens right now.

It's not easy but creating content is the best way, we have a blog at https://blog.e11.io that brings most of the leads for PRE-ICO investors.

Hope it helps clarify a bit,