The girl was in the family's back yard Saturday with her younger brother in the Kodak/Northview community in Sevier County, WIBR-TV in Knoxville reported.
The brother saw his sister being taken away by "a man," police said.
The girl's mother said she saw her daughter come from woods behind the home with her wrists bound with rope and some of her clothes missing. The girl said a man had sexually assaulted her.
The mother called police and the child was taken to the hospital, the TV station reported.
"One of the hardest parts of working with kids who've made allegations of sexual abuse is that we rarely do have DNA evidence, we rarely have medical evidence, so really all we have is the child's story," said Pamela Dickey of Childhelp Children's Advocacy Center of East Tennessee, adding the child's family acted appropriately in obtaining immediate help for the girl.
The sheriff's office does have DNA and other medical evidence in this case. The evidence along with the girl's story led to the arrest of the adolescent, who is being held in juvenile jail, the TV station reported.
It is not clear how police located the teenager in order to compare his DNA with the DNA retained as evidence.
It was also unclear from the sheriff's information whether the child knew her attacker, the TV station said. Childhelp said, however, most of those who harm children are close to them.
"The beauty of this case is that mom believed immediately and ran to get her treatment. So this child has a very good prognosis for having a good outcome even though this was an awful thing to happen to her," said Dickey, adding parents should be vigilant and believe their children if they say they are being harmed.