The main characters in Paper Towns by John Green are Quentin Jacobsen, Margo Roth Spiegelman, Ben Starling, and Radar.

Quentin is the main character and narrator of the novel. He is a high school student preparing for college who is also head-over-heels for his neighbor Margo. Margo is considered popular, while Quentin and his best friends, Ben and Radar, are not. These social differences play an important role in their lives.

The minor characters of this novel are Lacy Pemberton, Mr. and Mrs. Jacobsen, Mr. and Mrs. Spiegelman, Detective Warren, Jase Worthington, Becca Arrington, Chuck Parson, Gus, Ruthie Spiegelman, Myrna Mountweazel, Angela, and Dr. Holden. Without these minor characters, the drama between Quentin and Margo would not be as noteworthy.

John Green's novel, Paper Town, is an adolescent novel set in Orlando, Florida. The main characters are:

QUENTIN JACOBSEN. The protagonist of the novel, Quentin is a 17 year old boy who attends an Orlando high school. He is in love with his next door neighbor, Margo. 

MARGO SPIEGELMAN.  A longtime friend of Quentin, she shows up one night and convinces Quentin to go on a night of mischief around Orlando, which includes breaking into Sea World. Then she disappears. 

MARCUS "RADAR" LINCOLN.  One of Quentin's best friends.

BEN STARLING.  A good friend of Quentin, he is nicknamed "Bloody Ben." 

LACEY PEMBERTON.  She is Margo's best girl friend; Ben is her boyfriend. 

QUENTIN'S PARENTS.  They are both therapists.