That is a difficult situation. At 6 months the puppy is fully grown and if not fixed then the male does wander away from home moreso. It is sad that the owners are allowing their pup to do this. Not responsible owners
. Hopefully he will come back and be ok. I know that where I live it has been triple digets. No dog will get too far in this weather. My guess is that he is hiding in the shade somewhere in the neighborhood. I would tell the neighbors that you saw their puppy again in your yard at such and such time. They are going to be looking for him. Hopefully they will stop letting him out the front door. I don't think it is your responsibilty to take care of him, but I would try and get him if i see him, only because I would not want anything bad to happen.