Ebay selling my missing amplifier

If the OP received any monetary settlement with the shipper for the lost shipment then he no longer has any ownership claim whatsoever.

Contact the shipper, USPS, DHL, FEDEX, UPS and open up an investigation. I know USPS has an investigation team that deep dives this stuff in coordination with the FBI due to the criminal elements being involved. 

Above posts are correct.  If the amp was insured and you were paid the insured value, you have been made whole and have no title or rights to the amp.  The insurer is the amp’s owner and may or may not choose to take action.  The legal exposure of Cargo Largo depends on whether they are a bona fide purchaser, meaning they gave value for the amp without notice it might be being sold by a thief.

You could buy the amp with the insurance proceeds, of course, and maybe even come out ahead, if you can negotiate a good deal.

in 1973, my 1969 Les Paul Custom was stolen in a burglary.  I’m still looking for it!

@audioquest4life "I know USPS has an investigation team that deep dives this stuff in coordination with the FBI due to the criminal elements being involved."

That may well be but the FBI isn't going to focus on some potential one off maybe theft of an amplifier.

Was there a fire sale somewhere on crystal balls?