Update : BIL is fine, very sore, and very upset. They are going back out to look for Max. I emailed my MIL the flyer I made so she can print it out. Brads very upset over totaling an awesome truck and loosing his best friend.
I've had to look for the occasional lost animal. Here's my suggestions:
Have flyers made up. A printer can print them up for very little money. Make the paper a bright color but fluorescent paper fades fast. Plaster them at (driver) eye level around the main intersections in the area he was last seen for at least a mile. Make sure they will be noticed by drivers so think of the line of sight. Put them around schools in the area. Kids see more than adults. Put something in that makes it personal, that motivates the public to get involved and look out for the dog. Something like, "I lost my best buddy when I rolled my car (give location and date). Please help me find my best friend." Use a picture--it can be a black and white printing.
Take/fax the flyer to every vet, animal shelter and pet shop in the area. I would do this in person to make sure the flyer gets posted on the walls, rather than on the desk or in the garbage. Post it in grocery stores. Saturate the area for about three miles from where the accident happened.
Offer a reward, and put it in big letters.
Put an add in the newspapers' lost and found.
Contact the rescue he came from and give them a heads up. They might have some connections.
You need to make sure you are in constant contact with the animal shelters because some shelters only keep strays a few days. Also, any injured or sick animals are usually put down very quickly, even in non-kill shelters.
Check the lost and found, looking for any dog that even remotely fits the description. Some people are really bad at describing a dog accurately, even the size. Call them all and don't limit your search to just the area the dog was lost in. Dogs can travel a long way and sometimes people find a dog in one location and then take them home, far from where they found them.
Don't give up hope. Sometimes animals just get so shocked by something like this they go into hiding for a day or so. Sometimes people find them and it just takes awhile for them to start looking for the owner.
Last, but not least, once you have the dog back, go to all the places you put up the flyer and take them down--there's the issue of littering.