The key is sharing links to interesting questions and answers or even blogging about them. If any of you have blogs that people follow, consider telling a story about how a particular post helped solve a problem someone was facing.
In short, you'd need to find a way to create a need and then fill that need.
I also see Facebook as a means of promoting this site. Many of us have family that we've connected with on Facebook, and Genealogy and Family History definitely has a family aspect to it.
If you have a family member with a question about a past ancestor, for instance, you could either:
- Ask the question here yourself and then share the link publicly on Facebook with your family member.
- Encourage the family member to post the question him/herself.
I actually think #1 is better, as it requires no initial action on the part of the other party, but after seeing an answer that helps him or her, he/she may be more inclined to join.
I also think this technique could be used to engage the experts as well. If they ask a question in their blog, try to repost it here, without plagiarizing their work, of course, and then share the answers with that person via the link.