The boy, whose name was not released, told police he was fed only small meals while being restrained for months in the basement, The Kansas City Star reported Wednesday.
Police officers found the boy after the Missouri Children's Division sent them to check on him after receiving an abuse call.
The teen's stepmother answered the door and told police she would go downstairs and get him.
Police told her to stay upstairs while they checked on the boy.
They found him handcuffed to a post, wearing dirty clothes and looking frail.
He said he had been locked in the basement since Sept. 27 when his father removed him from his high school saying he wanted to home-school the boy.
Detectives said they have to research the family's background before submitting the case to prosecutors for review.