Oh no. I am so sorry. However, this happened w/my father's cat recently. She just disappeared. My Dad walked all around the neighborhood daily and told anyone he met that he was missing a cat. He especially spoke to children and the mailman (they're out and about more than anyone else). Three days after the cat went missing, people from a few neighborhoods over were coming to my Dad's to report sightings! The cat came home one week to the hour she went missing!
So there is definitely hope. Do talk to the mailmen/women in the area- they will probably notice if someone has a new dog. You and Gus are in my thoughts.