Authorities are still trying to find her mother, brother and a family friend.
Police have arrested 30-year-old Matthew Hoffman and charged him with kidnapping. The teen was found inside his Mount Vernon, Ohio, home.
The mystery deepens about what happened to Maynard's 10-year-old brother, Kody, her 41-year-old mother, Tina Hermann and Hermann's 41-year-old friend, Stephanie Sprang.
"We were hopeful that we would find more than one, but our information was definitely that mostly likely Sarah was going to be in that house," said Knox County Sheriff David Barber.
The four vanished Wednesday, the last time Maynard and her brother attended school.
Hermann failed to show up to her job at a Dairy Queen and blood was found at her home.
Investigators won't say what led them to Hoffman's home, but his mother and stepfather own a house within walking distance of the family's.
Hoffman's neighbors said his behavior was disturbing.
"My friend dated him and she just broke up with him like two weeks," one neighbor said. "He had choked her and she had marks on her from where he had choked her."
Authorities said they don't know if Hoffman had any connection to Hermann or Sprang.
He's not the ex-boyfriend of either woman, but police do believe he's the key to finding the others.