You should be sure people know about your race. Get as many listings as possible, consider buying listings, and definitely spread the word.
Here are some sites you can list with:
- Michigan Runner
- MichiganCrossCountry.com Calendar
- MichiganCrossCountry.com Forum
- RunMichigan.com
- Running in the USA
- Runners World
Most of those sites also offer paid advertising opportunities.
Leverage Facebook and Google Plus! There is nothing as powerful these days as social media — people will respond to an event that you create. Invite your friends (selectively — don’t invite people who don’t run) and more important than anything ask them to in turn invite their friends.