Check in the phone book and also with local animal control for the numbers. If you have the resources and can find one, there are actually pet detectives that will search for your animal. Many times these people have an effective network of sources to use. Be sure to check for references and what the charges will be. Fees vary greatly and you should ask about them if your animal is not found.
Many animals can disappear for months and then turn up.
Search daily and check your phone book for other ideas. Look under government agencies, pets, dogs, cats, animal behavior, zoos, feed and anything else you think relates to your pet or animals in general. Also, parks, malls, resort areas, grocery stores, post offices, businesses, schools, and other high traffic visible areas are good places to post flyers. Ask for permission or for a board where such items are welcome first. If you have not found your animal after several months then the outlook on finding them is getting bleak and you might not ever do so.