SEOUL - Earlier this year, a South Korean investigative television programme featured the story of a 19-year-old who died from cirrhosis, after working as an illegal sex worker for years.
The report revealed the teenager had run away from home after falling victim to sexual violence when she was 12.
Her alcoholic father, a single parent, had been physically abusive. She soon became involved in juvenile crime, was habitually intoxicated and was forced by other runaway teens to sell herself for money . The teen was just one of some 200,000 teenagers estimated to run away from home in the country every year.
Data suggests that many who do so also end up being forced into prostitution.
Statistics show that the illegal sex trade involving teenagers is rising, with lax rules on Internet and smartphone use raised as a possible reason for this.
South Korean law stipulates that both purchasing and selling sex carries a one-year penalty in prison or a fine of up to 3 million won (S$3,740).
Buying sex from a minor carries a heavier penalty of one year and 10 months in prison or a fine of up to 50 million won.
Despite the penalties, the number of sex-trade cases that involve teenagers more than doubled from 528 in 2010 to 1,290 last year, while the total number of sex-trade cases dropped - from 9,583 to 8,977 - in the same period, according to data released by the National Police Agency.
The number of teens who ran away from home increased between 2009 and 2012, from 15,114 to 21,813.
The government predicts that figure would reach 200,000 if it counted those who ran away from home but were not reported by their parents or guardians.
As of 2013, 60 per cent of teens who were forced into prostitution were runaway teens.
Nam In Soon, from the opposition New Politics Alliance for Democracy, said one of the reasons behind the increasing number of teens involved in the sex trade has to do with the government's "poor regulation" of Internet and smartphone use.
As of 2010, about 80 per cent of the sex trade with teenagers was pre-arranged online, mostly via instant messaging applications on smartphones, which makes it harder for the authorities to crack down on.
According to Ms Nam's office, 717 mobile applications were involved in the illegal sex trade in 2013. "Among 182 of the apps involved in the sex trade, 65 per cent did not require their users to register their age, and 96 per cent were free applications for anyone to use," she said in a statement.
Lax regulations against managers of accommodation widely used for the illegal sex trade were also considered a factor.
Last month, the murder of a middle-school girl by a man in his 30s at a motel room in Seoul received heated news coverage.
The victim had reportedly met the suspect for paid sex via a mobile messaging application.
Following the arrest of the suspect, a group of female lawyers filed a request to the police to investigate the owner of the motel.
"It is illegal for motel owners to let teenagers stay in their property without checking their ID," said Kim Bo Ram, from the Korean Women Lawyers Association.
"But 65 per cent of sex-trade cases involving teenagers take place in motels, according to data released by the Gender Equality Ministry."
Local studies have shown that female teens are more likely to run away from home and turn to sex work than their male counterparts.
In 2010, 13,462 female teens ran away from home, compared to 8,825 male teenagers, according to National Police Agency data.
Among the 175 female runaway teens surveyed by the Seoul Metropolitan Government in 2012, 41 per cent said they had been sexually abused at least once in their lives, while 55.3 per cent said they were involved in the illegal sex industry.
"The studies show that sexual violence and underage prostitution are linked to each other," said Kim Nan Hee, a Gwangju-based activist for youth rights. "This tells us that we need to look at the two issues together, rather than simply trying to combat sex trades."