Contributors and creators are going to be your best bet for becoming influencers or evangelists. Make sure you are taking care of these folks in your community strategy. Treating all of your audience equally is a strategy failure. Know what each of these groups is trying to accomplish on your site, and make sure you simplify the path to THEIR goal, which is not always the same as YOUR goal. But that's the social part. A conversation not an advertisement.
1. Discover who you are and how you relate to your community 2. Reveal how your community relates to you 3. Listen to your customers tell your story 4. Connect your inner circle of communities 5. Cascading communications in tiers