The standard response is "Hold it and they will come."
Remember, if just one person shows up it was a success. Which gives you the impetus to do it again, hoping that the second time more folks show up. If nobody comes do it again anyway to give folks a chance to think about what they missed.
Post it. Keep reminding folks as the date draws closer. Consider posting a running list of those coming. (Look at the posts for the monthly OC dinners in the Virginia/Richmond section.)