Thats a tough one there Janet!
Your only hope is if you have a match to the lost one so a guy could set up his rig on that specific signal, and really enjoys about an impossible challenge..if you are offering a pretty substantial reward or at least a good faith payment for trying, that would help.......You would want the other earring and have any potential 'contractor' show he can hit it..
We have all chased these kinds of efforts, only to find the item in a place way outside the supposed 'lost' area...are you 100% SURE you lost it on that path? If you are not, then theres really no hope from any of us... its completely lost...
It would be different if it was a ring, but a little stud earring is a whole 'nother monster to find for our limited capabilities on a mile stretch....it would be super hard to find it in even in a 10x10 sand area...
Although, a guy might go out at night with a black light flashlight of some sort and hope to spot the diamond irridescent glow....a diamond will glow blue under that light source...