The number of Britons identified as victims of human trafficking soared by more than 50% last year, the National Crime Agency (NCA) has revealed.
Social media and smartphone apps were being used by traffickers to recruit British nationals to sexually exploit them, while some victims were being "controlled" by drugs and alcohol, an NCA report found.
A total of 3,309 people, including 732 children, were identified as potential victims of human trafficking in the UK - a 21% increase on the previous year.
They included 300 Britons, up 55% on 2013, while the UK remained the most prevalent country of origin for potential child victims of human trafficking with 116 cases.
Caroline Young, deputy director of the NCA's organised crime command, said the figures showed that authorities were "increasingly encountering and recognising examples of trafficking in our society".
"Human trafficking is an insidious and complex crime where much of the exploitation is hidden from view," she said.
"The National Crime Agency is committed to continually disrupting this vicious criminal trade in human misery, which exploits the most vulnerable people, both here and abroad, for financial gain.
"Victims are being forced to work in private houses and in hospitality, farming, manufacturing and construction industries. In many cases, threats and violence are used to ensure compliance.
"The NCA will continue to work closely with a range of partners to help eradicate this vile crime."
Human trafficking is the movement of a person from one place to another deliberately to exploit them for reasons including labour, sex or crime. Victims are usually deceived or coerced into giving consent to be moved.
In its fourth annual report on human trafficking, the NCA said Romania was the most prevalent country of origin of potential victims of trafficking in the UK for the fourth year running.
The South East had the highest number of potential British victims with 51, compared with 34 in the North East, 31 in the East Midlands and 14 in London.
The NCA report said: "Some UK nationals trafficked for sexual exploitation within the UK have been recruited via the internet through social media sites and smartphone messenger apps, but also use these methods for arranging to meet males for sex.
"In many cases of UK nationals trafficked internally for sexual exploitation, potential victims report being controlled by the use of drugs and alcohol, stating that they were so 'out of it' at times that they did not know what happened to them.
"Another potential victim reported that those exploiting her had pictures of her that they threatened to 'show around'."
Some 298 victims of human trafficking were identified in London last year, followed by 289 in the South East, 235 in the South West and 226 in Yorkshire and Humber.
There were 193 potential victims in the West Midlands, 181 in Eastern England, 167 in the East Midlands, 133 in the North West, 67 in Scotland, 66 in Northern Ireland, 54 in the North East and 16 in Wales.
The remaining potential victims were recorded as being in multiple areas, overseas or their location was unknown.
Barnardo's chief executive, Javed Khan, said: "These figures are just the tip of the iceberg. We are pleased that more children are being identified as trafficked but we know there are many more who are missed.
"There's a long way to go until front-line workers are able to spot the signs and recognise the victims of this terrible crime. Barnardo's will continue to work with the relevant agencies to help keep these children safe and protected."