1. Have the animal scanned for a microchip. If microchipped, contact the registered owner.
2. Contact Animal Services to notify them you have found a pet. Call and send them an email with the date and location where the animal was found, a complete description (species, gender, sterilization status if known, breed or breed mix if known, color, markings, approximate age) and your contact information (e-mail and phone). REQUEST THEY SEND A REPLY ACKNOWLEDGING NOTIFICATION.
If possible, make a flyer including a photo and send it as an attached file. All other notifications should not contain too much detail (you want the caller to be able to provide relevant details to help correctly identify the owner).
3. Place a free "Found Pet" ad in your local paper - main and community - online and print.
4. Call Pet Owner's Alliance at 1-800-US-Stray, post notices on craigslist, www.lostpets.com, www.pets911.com, www.dogdetective.com, www.petfinder.com. Post flyers at local vets, grocery stores, pet stores, laundromats, and throughout the neighborhood and on posts at major intersections near the location the animal was found.
When someone contacts you and claims to be the owner/guardian of the animal, request copies of vet records, photos, etc. to prove the animal is theirs. If the animal is not current on rabies, county license (for dogs) and is not microchipped, explain the importance of these items, and offer to meet them at the Humane Society with the animal so they can have these services completed before turning the animal over to them.
If it is a highly adoptable dog and they refuse, tell them if surrendered to Animal Services (along with their name and contact information), they will be fined more than the cost of getting all three services at the Humane Society. This way the animal has some protection should it escape again.
Keep in mind, that it is almost always far preferable for an animal to be returned directly to its owner if it has one than to go to Animal Services. If you are unable to temporarily foster an animal, and do not know anyone who can foster it, consider asking your veterinarian if he or she will board the animal. Many rescuers have advance arrangements with veterinarians who allow them to board found pets (on a space available basis) at a discount.
Good luck!