Help!!

I found a Huge Newfie mix at the local mall in traffic last Fri. Took him to the vet, he was malnourished, but healthy. All my other (rescued) pets, cats and dogs, got along well. Thur. 2 days ago he got out the sliding door. Cannot find him have searched high and low. Ad hits the paper with reward today. Have canvassed the neighbors. We don't have many. Live on 7 acre wooded lot. NEVER have lost a pet. What's next? Have looke nonstop by car and foot. So much of the area is dense woods. Any other suggestions? I'm FRANTIC. Will soon be 48 hours. He was here 6 days. Could he find his way back? he seemed to want out alot, staring out doors, windows. If he had another home it wasn't much. To be honest I didn't run an ad because he was soo skinny and ragged, that IF he had a home they didn't need him back. Any ideas for a search? Vets, shelters, animal control have been called. He has collar and tag. I am at my wits end. Thanks