Has the cheque been presented, and has the "clearance time" he noted on the sale details passed? Assuming YES...
He's still posting/selling on Ebay, so I'd be inclined to make a formal complaint to Ebay that goods have not been delivered and there's been no response to your chasing him.
They may "freeze" his account or take other action.
At the same time, I'd alert Ebay and him that in X hours you will be making a formal fraud complaint to the police. I assume you have his address, since you sent the cheque there?