Now back home on the North Shore, she wants to dedicate her life to the cause.
Miss Clifton says the month-long trip, organised by Destiny Rescue, was life-changing. In Thailand, the group saw the red-light district, where they witnessed people pushed to visit sex shows.
Destiny Rescue estimates the Thai sex industry generates $4.3 billion annually. It says, worldwide, one child is sold into the industry every 26 seconds.
Miss Clifton says sex shows are popular tourist activities but people need to think about the background of the girls involved.
"The longer we stayed in Bangkok, the more I realised you can truly do anything in this country and no one will lift an eyebrow. It's like evil has taken root and has no plans to leave," she says.
She witnessed more of the same in Cambodia, where Destiny Rescue has set up primary schools and kindergartens so street children can receive free education.
The volunteer organisation believes having children in school reduces the chance they will be stolen and sold. When Miss Clifton visited the schools, she met children who had suffered horribly.
"What do I say to a 6-year-old girl who has been gang raped by 17 men? What do I say to a 6-year-old girl who days ago watched her father kill her mother?" she asks.
Miss Clifton volunteered in the Cambodian and Thai programmes, where rescued girls and women work in cafes, sewing, in jewellery factories and hair salons. But the process of rescuing sex slaves is complex and dangerous. A group of volunteer men go into brothels and act as customers, gain the trust of a girl and offer her the option to work in a rescue programme.
If the girls are willing, the volunteers help them to run away. In some cases Destiny Rescue buys them out of the brothels.
Miss Clifton says new volunteers are not allowed to go into the brothels because of the danger involved, so she worked in prevention and post-rescue work programmes.
She plans to return to Thailand in February to sit an English language qualification so she can teach in the rescue programmes.
Until then, she is working with a group of Aucklanders to raise awareness through a Facebook page and public talks. Miss Clifton has paid for her trips to Asia, and is raising cash to send money to the cause in Thailand. This includes selling jewellery and products made by the rescued girls.
The former Rangitoto College student, studying nutrition and psychology at Massey, says: "People may just think I am a fanatic trying to raise money but if this was their child, brother or sister how much harder, further would they want me to push?"
TO HELP
To support Shayna or Destiny Rescue, see: www.destinyrescue.org www.Facebook.com/choicetodosomething or email shayna.a.clifton@gmail.com.
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