Internet firms must do more to tackle human trafficking-related material, Theresa May said ahead of a meeting of her modern-day slavery taskforce.
The Prime Minister said the internet was giving traffickers a way to lure victims, enabling their "barbaric crimes".
Downing Street said criminal gangs involved in sexual exploitation were using the
internet to advertise victims on adult service websites.
Mrs May will meet ministers and law enforcement representatives on the modern slavery taskforce to discuss how to tackle the problem.
She will receive an update on work done by the National Crime Agency, Cabinet Office and data specialists from across government who are currently trialling the use of data analytics to uncover more victims of modern slavery.
By analysing internet sites which could be used to advertise modern slaves, this technology identifies ways in which offenders are operating online to exploit trafficked victims.
Mrs May said: "Modern slavery destroys the lives of some of the most vulnerable in our society.
"All too often we see criminal gangs coerce people with false promises of a better life, only to treat their victims as commodities for sexual exploitation.
"What is clear is that the internet is giving them the space to do this, and enabling these barbaric crimes."
Mrs May said internet companies "cannot stand by while their platforms are used to facilitate child abuse, modern slavery or the spreading of terrorist and extremist content".
"As the hosts of user-generated content internet companies can and should be doing more to prevent trafficking-related material from appearing on their platforms."
The Government wants firms to use their own technology to identify and remove adverts or websites linked to trafficking.