"The system has failed," Kardashian wrote. "It's heart breaking to see a young girl sex trafficked then when she has the courage to fight back is jailed for life! We have to do better & do what's right."
"The justice system is so backwards!!!" Cara Delevingne posted on Instagram. "This is completely insane."
Snoop Dogg posted a side-by-side comparison of the acts and sentences of Brown and Brock Turner, who had been sentenced to six months for sexual assault. He was released after three.
The calls to free Brown come as stories of sexual assault by powerful men have dominated the news, and after a slew of celebrities also took up rapper Meek Mill's case, who was sentenced to two-to-four years for a parole violation.
An online petition calling for Brown's release has garnered more than 200,000 signatures.
Last week, the Nashville Fox affiliate ran a story about Brown, and showed portions of a 2011 documentary, Me Facing Life: Cyntoia's Story, in which filmmaker Dan Birman explored Brown's familial legacy of abuse, and her own history of being sex trafficked.
"We started the conversation," Birman told the Fox affiliate. "This is a young girl who's at the tail end of three generations of violence against women."
Me Facing Life also helped spark a push in Tennessee to reform the state's juvenile justice laws.
During trial, Brown said a stranger, Johnny Mitchell Allen, had taken her to his home and had told her about his numerous guns. Brown said Allen reached under a bed for what she thought was a gun, so she pulled a .40 caliber handgun out of her purse and shot him. She then took two guns and some money from his wallet, and drove his truck to a Walmart carpark.
Brown was tried as an adult. The jury rejected her self-defence claim.
Derri Smith, CEO of End Slavery Tennessee, said Brown does not deny killing Allen, but is asking for her sentence to be changed to second-degree murder.
The advocate also highlighted the support from Rihanna, Kardashian and other celebrities.
"Think about Ashton Kutcher and the difference he has made around the issue of human trafficking," Smith said. "Celebrities can use their platform to begin conversation about societal issues."
Brown's supporters can help by sending letters to the head of the state's parole board and the governor, backing Brown's clemency petition, Smith added.
Had Brown been charged today, "she would have been seen as a victim. She would not have been tagged a 'teen prostitute' as she was in trial," Smith argued. "There is NO such thing as a teen prostitute. Any minor used for commercial sex is a human trafficking victim."
During her time in jail, Brown received an associate's degree. She has "served time and used it well, to help other youth raised similarly to her", Smith said.
