City of the Beasts by Isabel Allende

Alexander Cold, a fifteen-year-old California boy, is sent to stay with his grandmother in New York while his mother is being treated for cancer. After arriving at the airport to find no one waiting for him, he wanders through an alternate-dimension New York where no one will give directions to a polite out-of-towner, has all his belongings except his passport stolen by a girl around whom, had the plot not demanded it, he'd never have dropped his guard for a second, and eventually winds up at the door of his grandmother's apartment. Grandma Kate is a reporter for International Geographic, so of course she promptly takes Alex off on an expedition to Brazil, to track a yeti-like creature reported to inhabit remote portions of the Amazonian jungle. (This expedition is, of course, the reason his passport couldn't be stolen.) The Amazonian version is known simply as the Beast, and the North American version, i.e., sasquatch, or "Bigfoot," has apparently never been heard of, or at least is never mentioned. The Beast is also rumored to have a city, hence the title of the book.
Excerpt of a review by Elisabeth Carey
Review from: nesfa.org