On day 12 of searching for a dog in a heavily wooded area, distraught and hopeless, my friend ran into a couple of hunters. They said they lost the occasional dog on a hunt, but always got them back. What they told my friend has helped many dogs and families be reunited.
The dog owner (s) should take an article of clothing that has been worn at least all day, the longer the better, so the lost dog can pick up the scent. Bring the article of clothing to the location where the dog was last seen and leave it there. Also, if the dog has a crate & familiar toy, you can bring those too (unless the location is undesirable for the crate). You might also want to leave a note requesting item(s) not to be moved.
Leave a bowl of water there too, as the dog probably hasn't had access to any. Do not bring food as this could attract other animals that the dog might avoid. Come back the next day, or check intermittently if possible. Hopefully, the dog will be waiting there. My friend was skeptical and doubted if his dog would be able to detect an article of clothing if he didn't hear him calling his name as loud as possible for all day, for 12 days. But sure enough, the dog was sitting next to the articles the very next day.
I hope this helps someone out there who's missing a buddy. Good luck!