Someone stole one of our dogs when I was in high school. My mom was unloading my cousin from the van (he's in a wheelchair) and had let our senior mutt dog out to use the bathroom. She saw that the dog was in the horse pasture, by the fence (which backs up to a large ditch and then the county road), went inside to get my cousin settled in, got distracted-- and when she came out ~15 minutes later the dog was gone. Missy was blind, and a senior and never strayed very far from the house. In addition to being blind, she had mobility issues and couldn't get across the ditch, nor had she ever tried (think farm drainage ditch, quite steep and wide but never more than an inch or two of water in the bottom), which was why my mom wasn't concerned even though she was out of our yard and near the road in the pasture.

She hadn't wandered onto the road and been hit, she was too large to have been easily taken by a coyote, and she never turned up. We searched for her for ages. I still wonder what happened to her, even though it's been ten years and there's no way she's still alive. The only explanation is that someone driving by saw this sad old looking dog and "rescued" her.