Where can my tortoise be??

Hi, my tortoise has been missing for about a month now, he lived in our backyard, one day he was gone. We search just about everyday for him, we see no holes anywhere, our backyard is fenced in so I don't think he could get out. I just cannot believe he is still alive, we live in Yuma, AZ where it gets soooo hot. I would think that if he has passed, I'd find his body or shell somewhere? I just don't know what to do. Like I said we have searched everywhere. We have a grass in our backyard with sprinklers that go off twice a day, but I don't know if he'd be able to survive with that. Do you think he could still be in our yard?