Place flyers around your neighborhood and at the major road intersections where the pet was found. If you don't know the breed or the dog or cat ask a vet or expert to help you identify the breed. Call all vets in the area and report a found pet. If the pet has a tag, call the number on the tag. Both male and female pets that are not spayed or neutered are much more likely to go looking for companionship.
Cats can wear stretch collars with flat tags that are riveted directly onto the collar.
Keep cats indoors. When dogs are let outside, they should be in a fenced yard or on a leash. Leash laws apply to cats as well as dogs. Consider having your pet microchipped. Most vets will microchip your pet at a reasonable cost.