You can start by opening a Dispute as Item Not Received in the Resolution Centre at the bottom of this page.
You have already tried to Contact the Seller, so skip that step.
State that the seller is Not a Registered User (NARU).
EBay may insist that the dispute cannot be opened until the last estimated date for delivery, if, as you say, there is a note that the item has been shipped.
You can alternatively open a Dispute with Paypal.
PP allows disputes for 180 days from payment.
Same system. Remember to state that the seller is NARU.
The PP Resolution Centre is at the top of your PP account page under Tools.
If the seller does not provide proof of delivery (not shipping, delivery) you will be refunded.
Note that if the seller is new, or if he was already on eBay's radar as questionable, he may not have seen your payment yet, because PP has a Hold of up to 21 days against such sellers.