The main accused in an ongoing trial, Ho Bich Ngan, was just 17 at the time of the alleged crime.
She and two older partners opened a massage parlor in March last year in what used to be Long An Province before its merger with Tay Ninh.
They would post online job ads offering "food and lodging," targeting teenagers seeking work.
Through intermediaries, the group "bought" girls under 16 for VND7–10 million (US$270–390) each.
In May, two 15-year-old girls in Ho Chi Minh City contacted Linh to be recruited. Linh then informed Phuoc about the girls, agreeing to sell them for VND10 million each. The victims refused to become masseuses, but they were forced to sign debt documents, locked up and made to work off what the traffickers called their "purchase price."
One month later, two other teenagers were allegedly tricked in the same way.
According to Ngan's testimony, the parlor doors were locked from outside to prevent the girls from escaping, and if anyone did manage to get out, she would be caught, berated, assaulted, and have her phone taken away.
The police said the abuse came to light when officers raided the place and discovered the girls.
At the trial on Sept. 25 the victims authorized representatives to demand VND30 million ($1,200) in compensation for emotional harm.
The judges queried the defendants about their crime, saying: "These are human beings, not goods to be bought and sold," but the latter remained silent.
Ngan claimed she was a minor at the time and did not understand her crime, but now feels remorse.
Prosecutors said the repeated slavery of minors posed a "grave danger to society," and sought jail sentences of nine to 10 years for Ngan and up to 15 years for her accomplices.
The verdict is expected on Sept. 30.