What is the setting of Paper Towns?
The story is set mainly in modern-day Orlando, Florida, though Quentin does travel outside of that area. This setting is crucial to the story.
Consider the first section of the book, when Margo whisks Quentin off on their night of adventures. They visit specific stores that central Florida is known for, like Publix, as well as even more recognizable places, like Sea World. The downtown area of Orlando that Quentin describes as abandoned at night contrasts meaningfully with Margo's dreams of the vibrant New York, and the touristy nonsense that peppers International Drive plays a role in both Quentin's and Margo's sense of disillusionment with the world. Quentin's "pseudovisions" (subdivisions that were planned but never built) play a central role in the plot, also, and of course these are a real feature of modern-day Orlando.
Consider the weather imposed by the central Floridian setting, also: Quentin deals with constant humidity, intermittent rain, and predictable heat, all of which add to the tension he feels as he struggles on his search for Margo.
Margo and Quentin's immediate neighborhood, too, plays a role in the story: we know that they belong to a pleasant, safe, middle-class community, which makes their discovery of the man who committed suicide in the park all the more startling.