I need some advise on a shipping disaster.

I recently purchased a pair of speakers on Audiogon.  The price I offered was accepted and I sent the payment promptly.  The seller in return shipped the 2 speakers promptly and sent me the tracking numbers.  One of the speakers was delivered the next day and UPS has lost the other speaker.  The seller has put in a lost package investigation however UPs has not recovered the speaker.  It has been 8 days since the lost investigation has started.
I come to find out that the package was only insured for only half of what I paid for the whole package and it would cost twice that to replace the lost speaker new. So even if UPS cannot find the speaker and pay the insurance claim I cannot even replace the missing speaker for the amount of the claim.  
I'm not sure how to go about solving this issue.  I purchased and paid for a full set of speakers and only have 1.  
Any suggestion on what I should do next?  Has anyone ever experienced an issue such as this?  Does Audiogon have policies around issues such as this?

Thank you,

Please contact support@audiogon.com, Attn: Tammy if you want us to intervene. 
If you used a credit card, just wipe out the transaction with a phone call to your bank.   I suspect that 1 speaker is worth way less than the 2 you contracted for.   Can you even replace just one speaker of that type?
Hopefully the other speaker is on another truck and will be found. If you sell a pair of speakers for 5 grand you must insure them for 10 grand in case one gets lost or damaged because you will only be covered for the one that is lost or damaged. I hope all works out for you. Both speakers should be strapped onto a pallet then have shrink wrap around both of them to prevent losing one.
Having been through this from both sides as seller and buyer; the shipping company will only deal with the shipper as he is the one who paid for the service and their contract is with him. As he accepted your money with the good faith promise to provide you with a pair of speakers in whatever condition(s) were described, it is his responsibility to make good on the sales contract. I suggest you contact him and either agree on some set additional time for the speaker to be found or inform him you want a full refund and that he provide you the means to return the delivered speaker. If you paid with paypal they can help. If not certainly contact the audiogon Admin as offered above.