Thank you everyone for putting the word out! We ended up leaving the garage open just enough for a cat to get in, left out food, water, a litter box, and a small cat bed with my robe as bedding, with a security camera placed in the garage which emailed notification on motion detection. When we saw Zero laying in the cat bed, all we had to do was hit the remote to shut the garage door the rest of the way. If he'd been picked up I'm positive services like NoKillNetwork would have let me know!