Caroline B. Cooney's The Face on the Milk Carton tells the story of Janie Johnson, a fifteen-year-old girl who discovers she was kidnapped upon finding her photo on the Missing Child section on a milk carton. She recognizes her picture because of her curly, red hair.

Janie's best friend, Sarah-Charlotte Sherwood, is the owner of the milk carton upon which Janie sees her face. Janie misses Sarah-Charlotte when she is relocated to her birth parents' home, but Sarah-Charlotte lacks an inherent ability to deal with Janie's complicated problems.

Hannah Johnson kidnapped Janie when the child was three years old, but as a member of a cult, she was ill-equipped to care for the child. She left Janie with her parents, Miranda and Frank Johnson, whom Janie believed were her own parents. Miranda tutors students in English, while Frank is a soccer coach. They have great love for Janie and claim they did not know she was kidnapped and instead believed she was Hannah's daughter. Janie also believes this story when Miranda tells it to her.

The boy next door, Reeve Shields, is very close to Janie, acting as both a best friend and a boyfriend. Janie tells him about her alleged kidnapping early on, and they are sad to be separated by her move. Janie also has a good relationship with Reeve's sister, Lizzie Shields.

As the book progresses, Janie is reunited with the Spring family, from whom Janie was kidnapped as a young child.

Janie Johnson is the protagonist. She is 15 years old at the time of the incidents in the novel and is described as having bright red, curly hair. She discovers that she may have been kidnapped as a young child.

Reeve Shields is Janie's next door neighbor as well as boyfriend. Their relationship is very close in the novel, and Janie tells him everything that is going on.

Hannah Johnson is Janie's mother and, though she does not take part in the major action of the story, she is mentioned many times and plays an important role in the novel. She is believed to have kidnapped Janie from a mall.

Miranda Johnson is Hannah's mother and Janie's grandmother. She is an English tutor who studied literature in college.

Frank Johnson is Miranda's husband, making him Hannah's father and Janie's grandfather. We know little about him other than that he coaches soccer. He is not a major part of the action of the story.

Lizzie Shields is Reeve's older sister who helps Janie make an important decision at the end of the book.

Sarah-Charlotte Sherwood is a flirtatious teenager who claims to be Janie's best friend but often prefers to discuss boys over Janie's issues.

The Springs are the biological family Janie was born to and supposedly kidnapped from.

Janie Johnson: protagonist; red-headed, introspective, not an attention seeker; despite everything she's been given in life (and the fact that she's an only child), Janie does not act spoiled.

Frank and Miranda Johnson: the parents who raised Janie; they provided her with everything she could possibly need or want.  Despite how much they provide for her, they do not spoil her; they seem older than most of her friends' parents.

Reeve Shields: Janie's next door neighbor and love interest; good looking, good listener, protector; he and Janie are good friends before they become romantic with one another.

Sarah Charlotte and Adair: Janie's girl friends at school.

Hannah: Frank and Miranda's daughter; involved in a cult; identified as Janie's real mother, but likely kidnapped Janie at a young age.

The Springs: a red-headed family from whom Janie believes she was kidnapped; the book ends with Janie contacting these people and identifying herself as their "daughter...Jennie."