Tracking is nice for the warm fuzzies, and it's fine to ask your seller for the date and the service used for sending.
But if it has been:
More than 15 days from purchase in Europe
More than 20 days from purchase in North America
More than 30 days from purchase in Asia
And your seller does not respond usefully*, go to the Resolution Centre at the bottom of this page and open an Item Not Received dispute.
You will already have contacted the seller so go to Step Two.
If the seller cannot prove that you have received the item (the sole purpose of that tracking number) then he is required to refund you in full.
*An offer to resend an item is a SCAM. You want your money. Then you can decide whether to repurchase from that seller. Or not.