Include a recent picture of your dog (color, if feasible), your phone number, and a short description of where and when the dog was last seen. Include the dog's name and offer a reward, but don't specify an amount. If the reward is too low, people might not bother and if it's too high, they might think the dog is valuable and try to sell it. Also, duplicate the information in newspaper lost-and-found ads.
Try and hit all the public bulletin boards you can think of—community centers, dog parks, grocery stores, and phone poles in your neighborhood. (Be conscious of posting laws in your area. It'll be a waste of your time if the poster is removed.) Ask local merchants to display your ad in their display window or next to their cash register. Give stacks of flyers to friends and family and have them go door to door. Give the flyers to postal carriers, UPS and Fed Ex delivery people, and anyone else you know who gets around the neighborhood in their daily routines.