More Pandemic A-Fic: Scavenger by David Morrell, 2007, 9781593154417. Backdated to correct year.
A sequel to Creepers. Not really a sequel though, just the same characters.
Frank Balenger's girlfriend goes missing and is kidnapped by the Game Master. Frank follows clues from NYC to Montana (Wyoming? Idaho? North Dakota?) where a mining ghost town and the surrounding area are set-up like a game board. Frank and several other people have explosive necklaces and have to work together to solve a puzzle.
I recall this being pretty decent but the bad guy Game Master is some super-rich dude with all sorts of dastardly plans and powers. I generally don't dig those kinds of bad guys.