Missing box that required signiture?

I recently bought an expensive item on eBay and get it shipped to me via USPS, the package never arrived and I open a dispute on ebay, however the seller sent me the USPS tracking number and the signature of the the individual who signed for it but it wasn't me. What can I do? I have the full autograph of the recipient beside his signature.

Answers: Call the police. Or try to track the guy down yourself.