Interactive

Typically, these types of events are fundraising initiatives for a variety of worthy causes, i.e. MS, Cancer, local hospital, etc. These types of events normally have very good participation rates if for no other reason because people generally enjoy helping out the less fortunate.
Obviously, a good way to raise awareness would be some above-the-line methods (i.e. print, radio and TV spots). Once people know about the event, the next step is to somehow encourage them to register for it. The emotional appeal should be enough for some. For others, a more personal incentive may be required. Think about incorporating an instant-win or sweepstakes promotion tied into the registration process (i.e. each registrant receives a sweepstakes entry or chance to instantly win a prize). This would certainly increase the excitement surrounding the event and may have a positive effect on the number of registrants.