Don't give up hope. Last year my one of my dogs,( a small shih tzu), disappeared from my garden and I was distraught.
I never let them out alone and I was in the kitchen overlooking the garden and never heard a thing so I can only assume someone had nipped over our six foot fence and taken her.
It was freezing weather and as she is a real lap dog I was very upset. We did all the usual things..posters, police, etc etc. Despite being chipped too we heard nothing at all.
However, some time after I was in a taxi and was telling the taxi driver the story of my missing pet shih tzu when he suddenly said " Is it one like that dog there?"
I looked in the direction he was pointing and there she was scurrying along a main road being chased by a boy. It was a case of follow that dog! The lad fled when he realised we were after them. We cornered my dog near a field and she literally leaped into my arms. She was thinner, filthy but safe! I would not have ever believed the chance of finding her like that but it happened.
I have no real idea where she was during her absence but my purpose for repeating this story is that I got her back and hopefully you will be reunited with your dog too. I feel for you and wish you all the best in your search.
Pester the dog homes near you too so you keep your dogs description in their minds!