First, if you are sure it is lost, take it in and keep it secure so it won’t wander off. Don’t let it get back on to the street. If it’s wearing an ID tag, call the owner. If it’s wearing only a license call the public shelter in the community that issued the tag. If you have the time, take it to any veterinary hospital and have them scan for a microchip ID. If it’s impossible for you to keep it, bring it to the local animal shelter. If you prefer to keep it until its owner claims it, call the shelter anyway and have them register the pet as found, together with your name and address. If the owner checks the shelter’s found-pet registry, he or she will find your name there.
If the pet is collarless, don’t automatically assume it is also ownerless. That goes for its general condition as well. It may have left home in good shape, but who knows how long its been running around. Try not to automatically make moral judgments about the pet’s owners before you get the facts. Don’t adopt it as your own or give it to someone else before you do everything you can to find the owner. Run an ad in the newspaper (many newspapers offer free found ads). Read the lost-and-found ads, including as many back issues as possible (your local library should keep copies of the papers in your area). Keep in mind that a pet you have found may have been lost that very day. If its owners were to wait a few days before placing an ad in the local paper, it might be three to five days before their ad would appear.
Keep your eyes open for posters. Ask around –paperboys, mailmen, and delivery people. If you are so inclined you can take a photo of the pet (or a drawing) and make some “found” posters of your own. Contact vets and groomers.
Article from http://sherlockbones.com/index.html
