Somebody is playing a mean trick on you and you need to get to the bottom of it. Check all the walls carefully for fresh paint: That may be a sign that someone has made a hole in the wall and hidden your ipod in it and then filled the hole in again. Also, if you have floor boards, you might want to pull some up and see if it is underneath. If you have a concrete foundation, or tiles, then its unlikely to be in the floor, although you never know. This is really terrible. Has anything else gone missing? Or is it just the ipod? A good place for an ipod to hide is in the water tank above the toilet. It's kind of yucky in there though. Actually, I heard that Apple programmed all ipods to just automatically get lost after a while so you would go and buy an iphone or an ipad instead. That makes sense when you think about it.
First, find something that is your brother's/sister's if you have one. Then find yours and look in its case. I found mine by seeing my sister's sunglasses, then looking in my sunglasses case.
Start by looking where you had it last.