Jimmy Stone's Ghost Town by Scott Neumyer

With his new friend, David and his dog, Trex, by his side, Jimmy Stone discovers that the woods beyond his backyard hold the key to a world he could never even imagine. Soon, he ends up in Ghost Town, where he’s greeted by his ghost guide, Gasp, and receives an ominous prophecy.
Suddenly Ghost Town becomes as scary as it sounds, and Jimmy Stone realizes that he's in way over his head.