Ebay selling my missing amplifier

No they don't. I shipped a speaker by FedEx and it disappeared. They contract third party companies to make deliveries and the only "proof of delivery" is a piece of paper that says Delivered. No accountability, no investigation, no payout. 

The paper said Delivered. End of claim. 

eBay has a security department that can be reached by the sitemap. In the past, at least, they have had attorneys, former prosecutors with experience, on staff. You would need at least the listing number of the article you believe to have been your stolen property and probably any identifying information to verify your claim: insurance claim information, police report and any documents pertaining to the item in question (warranty papers, original boxes with serial numbers, etc.) If you were paid for your losses, your insurance carrier may have an interest, if you suffered partial loss (insurance deductible, e.g.) you obviously have an interest as well.  If you know where the article is being sold from and are able to contact local authorities there, that may be another option.

Not so I retired from U.P.S. High value shipments usually over 5000 are put into cages, and must be signed and scanned.  The driver or loader puts it on the plane, truck or trailer, and it is scanned again .They can locate a package by the last employe that scanned it. They know at all times where the packages in there custody are. You can't just pick it up and throw them in your trunk. It gets traced to you the minute it goes lost. Even non insured packages are scanned at every destination. They get scanned as they go around the belts inside the U.P.S complexes BIG BROTHER IS NO JOKE. They will talk to you if things get lost. And Fedex is no different as they copy from us.

@macg19 -- Wrong. You have no idea how high value packages are handled by major shippers.

BTW, I had a total of one package "go missing" while it was in the UPS system. It was insured. They could not prove delivery (and their software knows where every package is during transit). They paid my claim.

Much later I was informed that it was found in a UPS substation where it had been set aside for reasons unknown. It had been sitting there for months, unnoticed.

I have no idea how high value packages are shipped? Wrong again @wesheadley 

I'm an executive at a medical device company. We ship large, very expensive devices across the US and around the world every day.

Things get lost, damaged during shipping, scheduled pick ups for RMAs don't happen, and getting paid on an insurance claim is nearly impossible and requires a ridiculous amount of time and resources. 

Buying insurance often just means they'll look harder for your missing package.

You were lucky with your one experience with a UPS claim.

I also have one personal experience with a UPS claim for damage in transit, and they refused to pay it even with extensive photo documentation.