Look up. Follow all power cords to their highest points. Look behind tvs and computers on the power cords. In closets on clothes hangers, anything that could be a potential "tree" to your chameleon. Good luck, keep us posted.
:/ That's not good. Try to look everywhere he might have gone, and places that seem a little far-fetched. If your house is cold he might be in the warmest room or something. Also how did he get out and are you sure he's gone? I've thought lost my cham but he was just under my nose or something.
Be precautionary. Close toilet lids so your chameleon does not drown. Don't leave out large tubs of water or anything extremely hot that your chameleon could potentially burn themselves if they walk on. Good luck.