Just in case you might have washed and dried the socks with other garments.
If you dried it in a clothes dryer, it's probably stuck inside of one of your other garments that you dried at the same time. Check the body of the garment, sleeves, legs, etc. You may find it there. I find socks inside of shirts, etc. all the time (not PD socks as i wash my wool separately and lay flat to dry, and so don't use a clothes dryer).
However, this very thing did happen to me once, when i had a "brain cramp" and put my PD socks in the same mesh laundry bag that my other worn/dirty/stinky clothes go in and then washed and dried them together. The socks actually made it through 'ok' and are still serviceable. In fact, i'm actually wearing that exact pair of socks as i type this Post.