Updated November 25, 2017 01:53:01

Photo: A petition was set up to free Brown, who was jailed at 16 for killing a man she had been pimped out to. (Supplied: Change.org)

The story of a 16-year-old girl who in 2004 killed a man who picked her up for sex is spreading around the world, after a number of high-profile celebrities joined a campaign to free her.

Cyntoia Brown was sentenced to life in prison over the killing of 43-year-old Nashville real estate agent Johnny Allen.

Allen picked her up off the street after she was forced into sex work by her boyfriend, a pimp who went by the name "Kutthroat" and serially abused her, the BBC reported.

Brown said after he picked her up, Allen took her to his house and showed her his gun collection, telling her he used to be an army sharpshooter.

She said when the pair got into bed, "he grabbed me in between my legs — he just grabbed it real hard … I'm thinking he's going to hit me or do something like it".

Allen then turned over in the bed, and Brown said she panicked, thinking he was reaching for a gun.

Thinking she was about to die, she shot him in the head with a .40-calibre gun that Kutthroat had given her.

Brown was arrested for murder and tried as an adult. She pleaded self-defence. The jury found her guilty of first-degree premeditated murder, first-degree felony murder, and aggravated robbery.

She will not be eligible for parole until she is 67.

Brown's case has gone viral on social media after singer Rihanna posted about it on Instagram.

"Imagine at the age of 16 being sex-trafficked," she wrote to her 58.2 million followers.

"Did we somehow change the definition of #JUSTICE along the way?? Cause … Something is horribly wrong when the system enables these rapists and the victim is thrown away for life!"

Supermodel Cara Delevingne shared the post to her 40 millions Instagram followers.

Kim Kardashian West also tweeted to her 57.2 million following about the case, saying "the system has failed".

"It's heartbreaking to see a young girl sex trafficked then when she has the courage to fight back is jailed for life!

"I've called my attorneys yesterday to see what can be done to fix this."

Brown has since earned her Associate's Degree from Lipscomb University while in prison and is currently working towards her Bachelor's Degree.

She is also reportedly working side-by-side with the courts and the Juvenile Justice system as an unpaid consultant.

Assistant District Attorney Jeff Burks, the man who jailed Brown, said being young and likeable should not exonerate her.

"She wasn't just somebody who made one mistake," he said, according to the BBC.

"She was a very dangerous person. The choices she made were hers. She's pretty and smart and articulate so people have decided to take up her cause. Let's not forget her crime."

Topics: crime, law-crime-and-justice, arts-and-entertainment, sexual-offences, murder-and-manslaughter, united-states

First posted November 24, 2017 19:37:32