Good advice with the scent. However, some messages interpretable by humans are also a good idea:
Notify all local authorities including: local police, state police, local animal shelters, veterinary offices, trail maintaining personnel
Make fliers, with a color picture. Include a thorough description, your contact information, alternate contact info, and a reward offer. Post them at the trail head and anywhere else people can get to - like the shelter. Be sure to mention any pertinent health issues. For ease of contacting you, might not be a bad idea to make those little slips at the bottom with a phone #, so that someone can easily rip one off. Also post them all over likely towns.
A couple of other possibilities:
If your dog is an intact male, and you have access to a bitch in season, set up camp where you last saw your dog for a few days. The scent will typically draw in an intact male.
If your dog has a special dog-buddy - do likewise. They may home in on each other.
Best of luck.