Offer money, fame, world travel, plenty of food, and gear to test and use.
Seriously though like CG said what type of people you lookin for? just friends to hang out that have common interest in racing, do you wish to start an organized club or race league,
Usually every town has a free paper like here we have "The Shopper" which has an ad section read by many different people in many business and public markets and housing complex's like were I live. They drop a few off weekly in our laundry room. Maybe toss an add up for a week or two and see who contacts you.