Look on his feedback page. There should be a Contact Seller link on the right.
Or go to your Purchase History. Contact Seller is one of the choices in the dropdown menu on the right.
If worse comes to worst, start a Paypal dispute for non-receipt. That will certainly get his attention.
However.
Where is he?
From USA and Canada allow 14 to 20 days for delivery.
From Europe allow 10 to 15 days for delivery (yes, strange.)
From Asia allow 20 to 30 days for delivery.
You can start a dispute for 45 days after the transaction. Do not allow this to go past 42 days,though.