Thank you guys so much for the support. I've been back up and down that road twice- to and from work today- and there was no sign of him, thank God! I was so afraid that I'd see him in the road. I hope that he found his way to someone's house or either his owners drove around looking for him and found him since he was definitely well cared for, clean, neutered- I could tell.
It makes me wonder if either one of the dogs I have now ever got out, if they'd be that skittish to run away from everyone. With Crystal, my black lab, I knew there was no way she'd ever go to anyone. She was always super nervous around other people. And I guess Spike just stuck by her side so when people called, if she didn't go he didn't either. The two I have now are super friendly and I think they'd be in danger of being stolen because they seem to go to anyone.
I don't now which is worse. Too friendly, or super skittish....
Edited to add: There's nothing on Craigslist about a missing dog fitting that description. I may post a note on there about seeing him just in case.