Most dogs do return of their own free will and if not most are reunited with their owners after a short space of time. The local dog warden retains reports of lost and found dogs.
Stray dogs may still be handed into a police office and therefore you should contact Police Scotland by dialling 101 to ascertain if your dog has been handed in.
If your dog has not already been micro-chipped it might be something to consider.
See websites in related information for more help and advice.