What is the title of this YA fiction book from '90s?

There was a series of books, I think they had something to do with "the game." They were kind of like Christoper Pike & R.L. Stine books, scary/thrillers, and a group of people who, I think, played a game. There was a guy, who I think started out like their tour guide on the game, but was later after them? I cannot recall what these books were called and I don't have enough to Google - HELP!