Here's some tips Ive seen or heard off that weren't mentioned:
If you have a cat, watch it closely
Try to go in the room at night with no light or noise
Possibly try the flour trick
Look for warm, dark, small places
Double/ triple check your rack, Ive heard of people putting their snake back in the wrong container And because they can hide in the rack too
Most importantly, if it looks too small for them to hide in or get through they probably can. So look everywhere, I mean everywhere! They can climb alot too!!!
Good Luck and keep us posted