'Someone's knocking': Murdered 12-year-old's last text to mum an hour before her brutal death

A 12-year-old schoolgirl was brutally murdered in her motor home after telling her mother in a text "someone's knocking" at the door.

Yhoana Arteaga had been off school recovering from a leg injury from skating and had met her mother for lunch on August 10 in the US state of Tennessee.

The high school girl later sent her mother a text message referring to a visitor around 5.30pm.

She was found dead just over an hour later.

A 12-year-old Tennessee schoolgirl was brutally murdered in her motor home. Picture: Liberty Collegiate Academy

Her mother made the grim discovery when she returned home with her other two children.

Police have told local media there was no sign of forced entry, and believed Yhoana knew her killer.

Lieutenant William Mackall did not provide details of the cause of the girl's death, but told WKRN: "I've never seen anything this brutal in my entire career.

“An examination of the crime scene, as well as autopsy results, shows that Yhoana was brutally murdered,” Metro Nashville Police spokesman Don Aaron said in a statement.

“Without being overly specific, there was blunt force trauma to her body.”

Police did not confirm if Yhoana was sexually assaulted but her clothes were reportedly in disarray.

Those who knew Yhoana said she was as a "kind, polite, caring, fun, intelligent and beautiful" girl, according to the GoFundMe account set up to support her family.

The murdered teen sent a text to her mum saying someone was knocking on the door, an hour before she was killed.

"She will be remembered as a wonderful daughter and great friend to all who knew her," the page said.

Her Nashville school, Liberty Collegiate Academy, shared a tribute to the youngster on its Facebook page, with a picture of Yhoana using a laptop.

It read: "Our hearts are broken as we mourn the loss of Yhoana Arteaga, a 7th grade student at Liberty Collegiate and treasured member of the RePublic family."

"We love you, Yhoana."

The GoFundMe page has already exceeded its $10,000 goal by raising more than $12,600 to support the "hardworking" family.