How do you find a lost ball python?

Most of the the time they will hide in obviously, dark and warm places. Your water heater, the warming drawer of the stove, the back of your refrigerator. Or sometimes I have even been told , inside your furniture.
If all else fails Just wait it out and when the get hungry they will come out of their hiding places.
Here's a trick. Put a rat in a minno trap and put a bunch of plastic bags around it, if you are a light sleeper you will wake up in the middle of the night hearing the rustling of the plastic bags, and wham!! You have your snake.