The old saying of "aim small miss small" is truer than ever in interactive marketing.
Want to reach a whole lot of potentially interested customers? Search blogs, forums, followers, fans and buzz "ers?" that talk about your thing. Take that group and filter them down to the ones who talk and people listen to, engage with and spread their message. The ones that introduce new ideas and ways of doing things. The ones who articulate what you think about your business even better than you do. Then, filter a third time to ensure your really getting the super-influencers of whatever your thing is, not because they have more fans, but because they have more engaging fans.
Then earn their support. They're your long lost tribe founders.