Bear in mind that some citizens are loathe to take a found animal to the shelter right away and will keep it for several days or longer before turning it in. Consider using a trained tracking dog. Contact local obedience class teachers and inquire about hiring someone with a dog with Utility Dog certification to locate the cat by scent. Don't give up. Keep looking in those same old spots, calling and listening.
Cats are tough customers and can last many days without food or water.
They also can hide very well, remember, and may not be rescued by animal control or a citizen for many weeks after their initial disappearance. Don't give up as soon as the cat fails to return home or after only a few days and don't just wait for the cat to come back or not. Keep looking and keep checking. My cat went back to our old apartment twice in 4 months, and then had trouble finding his way back to the new place, so he just stayed.