Look around water heaters, under refrigerator and behind it. Look under and behind stove, washer and dryers. These are the first places I looked when I lost my snake. She had an 11 hour head start before I noticed her missing so I wasn't sure what room she was in. But since she had eaten a few minutes before escaping I figured she was still in my bedroom where she is kept. I taped a window screen over my doorway and searched everywhere. On the third day I removed the wall in my closet where our hot water heater is and a few minutes later while putting away clothes in my closet I looked down to see her going into my closet! Either she was back there, came out and was going back. Or she was somewhere else and decided to go back there.
Also one other thing I kept my house very cold the whole time she was missing so that she would be more likely to search out warm places. I made a bunch of little box hides and set out some heat lamps and pads in a few rooms and also left the lid off her cage just in case she might go back in there to get warm.