Seven suspected child trafficking victims were rescued in Northern Ireland over the last four months, police said.
Nine women and three men were also freed by officers probing the “hidden crime”.
Victims often have no access to medical treatment, live in over-crowded houses and cannot keep the money they earn, specialist officers said.
PSNI detective chief inspector Mark Bell said: “It can be hard to believe that this type of crime exists today but it is all too real, especially for the victims.
“They are often afraid to speak out or unable to report their ordeal to police for a number of reasons including language barriers or simply because they are held captive.
“It’s for this reason we all need to work together to help victims and stop this unacceptable crime.”
The PSNI has a Modern Slavery Human Trafficking Unit (MSHTU) and is supporting the UN’s World Day against Trafficking in Persons on Monday.
Mr Bell said: “I would appeal to people to be aware of goings-on in their communities and keep a look out for a number of tell-tale signs.
“These include people who can’t produce their passport or personal documents, who appear to be under the control of others or who have unexplained injuries, live in over-crowded accommodation or those who appear not to have any cash as they are not allowed to keep the money they earn.
“Modern slavery and human trafficking is a priority for the PSNI and our unit was established on April 1 2015 to provide a dedicated proactive approach to tackling this complex crime.”
He added: “Victims are often afraid to speak out or unable to report their ordeal to police for a number of reasons including language barriers or simply because they are held captive.”