I think your "backpacker who walks across a border or a mining surveyor" example is more than possible, but I expect the numbers of those to be very, very small. DHS/DoD/DoS has the means to ascertain the location of most AMCITS on international travel. Internet access and cell phone usage makes that job a LOT easier. Ask any LEO how a growing number of crimes are expeditiously solved now using cell phone data . . . .
Ok, I don't disagree with anything that you and
@GroundPounder said but, in my head at least, that's still after the fact stuff. If someone says, "find me Steve Smith" we could figure out his cell phone ids, his credit card info, passport #, and probably pretty quickly find him in the western world provided that he's not trying to stay hidden. If he's just a guy on vacation in Paris who maybe disappeared we could probably find a trail via those methods. But can those methods be used the other way to identify folks needing evac? I'm sure you could see the traffic and make some guesses but how often are people using their AMEX in AFG? What if they have a local burner phone as opposed to the one on their Verizon account? Im sure actual answers to this quickly end up in BEADWINDOW territory and I'm not trying to go that way.
Are we trying to recover backpackers, NGOs, private company folks who happen to be US citizens or just USG folks? Individual citizens sometimes go places that you or I likely wouldn't go...like the guy my wife went to college with who ended up locked up in North Korea or folks who get locked up in Iran, Mexico, etc.