Ouch, grab a magnet from autozone and fish around! the only place it could of gone is down because of our friend gravity. If you cant snag it with the magnet below the camshaft, then im sorry my friend pull the oil pan and remove it because thats where it is. If you dont get it outta there, it could cause some siereous damage. This has happened to me, thankfully the rod was hanging on by a thread of metal.

 

Ouch x 2 !

As C-guy says .. the pan might have to come off. You don't want to have that flying around in and around the rods and crank. BUT first .. you might want to pull the intake .. if fishing-around with a magnet does not work.

 

a long shot, but if it's in the pan, you might try to fish a thin flex magnet through the drain plug.