The only factoid I can bring to this discussion is that years ago data seemed to show that children tended to hike uphill. My experienced is a bit dated so I am not sure if this is still the case. Any search operation is better informed if the personal characteristics of the victim can be considered, and it seems that this is the case in your operation.

Hang in there. Any long term search can seem quite hopeless (and of course quite a few are) but many turn out very well, even when the "odds" are contrary. Good for both of you for getting out there and making a difference- may you have a glorious Sunday.