I would visit him in person &, if he is out, leave a stern, but polite, note in his mailbox with your telephone, cell & email contact info requesting that he contact you within 48 hours or you will need to seek assistance from law enforcement. (Make a copy of the note in case you need to take the additional steps below.) Yes, rep watches are technically contraband & frowned-upon legally, but I believe outright theft trumps contraband. Additionally, if you paid him any money (deposit, downpayment, etc) with a major credit card, contact your bank & ask them for assistance. If the guy is in business, he does not want to jeopardize/lose his vendor status with the credit card company.
If, after 72 hours (yes, give him 1 additional day to respond in case he is sick or out of town since it is that time of year), you do not receive a response, I would either send him a copy of the note you left previously in his mailbox via registered mail (so he has to sign for it, which will make it clear that you mean business) & wait an additional 24 hours for a response or take all the paperwork you received to your local police & let them do their thing.