In the evenings, keep the lights low and the house quiet and look under EVERYTHING with a flashlight. They can climb quite well if there are rough surfaces, like wood, clothing, etc. They won't climb vertical or smooth surfaces and more than likely will stay low.
You can try dropping the temp of your house and creating one basking spot with a heater in the corner, don't use a light or they won't use it. Try putting his favorite hide under a basking red or black light in the corner and cooling off your house.
Also, are you sure he got out on his own? Do you have a cat? They will eat lizards.
Day 10051 of life as a human on this planet... but who's counting?