... dog warden service.
Your local animal shelters/stray kennels.
Kennels and shelters in surrounding areas, in case your pet has wandered out of area.
Register your missing pet on websites such as Doglost ...
If a dog is thought to be of the type it can and often will be seized and conveyed to secure kennels.
If the dog is in a public place a police officer or officer appointed by a local authority ...