oh no i hope he turns up soon!! our neighbours (who are luckily retired so generally home) catch our escape artist of a dog all the time. does he talk to strangers or run away? thats our biggest issue with ours, shes scared of strangers so wont let them catch her, she thankfully knows our neighbours so will go with them.
i would definately door knock and ask, even if they have just seen someone catch ur pup and to take him to the local vet or pound. get those posters up, ive got everything crossed for you