hi there-- first of all- i feel your pain. have a snake escape can be the frustrating thing ever!
when looking for him id just look in dark secluded places. anywhere from the hamper to under a pile of clothes to inside baggage, closets, under appliances in kitchen, and (god forbid) in the venting. ive had escapes twice. once i found steve under the wine cooling fridge and the other time i found evita in a pice of baggage in a closet.
at night iveread its good to cool the house down a little provide hotspots such as heat panels or even heating blankets near places you think your snake might hide. ive heard of leaving flour or cornstarch on the floor near possible hiding places to track the snake thats especially hard to find. cutegayjason (an awesome guy on youtube who breeds chondros and owns pretty much ever other kind of snake) said he once had to have a professional come in and tear up his heating duct-- the little guy was hiding in there.
if you cant find him today... relax, take a deep breath, and i hate to say it but--- wait--- until tonight. ball pythons, as well as iot of other species of snakes are nocturnal and more active at night. theres a good chance with a flashlight in tow you will find him more easily at night, hiding, roaming, or exploring.
good luck-- ill keep my fingers crossed for you!