Help! my indoor cat got outdoors!!! where couldd he have gone?

hes done this twice before, and both times hes never left outside a 20ft radius of my house, he is mortified of all things outside (thunder, rain, toads, large birds, medium birds, loud noises, other cats, dogs, lightning, are all things that will make him jump and run back inside) but ive looked everywhere and im just not finding him! (if ur wondering why im panicing right now, its cuz our neighbors have a history of cat poisoning/shooting) i dont know what else to do, im stuck babysitting right now so its not like i can mount a search party for him, but im just asking fior some advice on where he may have gone, so, its 90 degress out, about to rain, and ive already checked my garage, im just looking for general advice to where i should look, anything would be helpful.