Actor Ashton Kutcher delivered an emotional speech on Wednesday about combating child sex trafficking before a U.S. Senate committee, in what he called his "day job" as an activist and technology investor.

Kutcher spoke at length about the challenges involved with ending child sex slavery both in the U.S., where it is facilitated through the dark web, and abroad, where children in disadvantaged countries are forced into the sex trade. He also dismissed those who might suggest he stick to his "day job" as an actor.

"My day job is as the chairman and co-founder of Thorn," Kutcher said, during an emotional 15-minute speech. "We build software to fight human trafficking and the sexual exploitation of children."

Kutcher added that his other day job is as the father of a two-year-old and a two-month old, whom he is raising with wife Mila Kunis. He told Congress he wants to make sure all children have the opportunity to pursue their own happiness, whether they're born in the U.S. or overseas.

The 39-year-old actor, activist and technology investor said he's seen things "no person should ever see" through his work at Thorn, where he's helped develop software that prioritizes child sex trafficking cases for police.

"I've seen video content of a child that's the same age as mine being raped by an American man that was a sex tourist in Cambodia," Kutcher said, in an apparent reference to his two-year-old. "And this child was so conditioned by her environment that she thought she was engaging in play."

Kutcher says he was "devastated" when he saw that video, and frustrated that his organization didn't have a tool to help save the child. "It haunted me because for the next three months. I had to go to sleep every night and think about that little girl that was still being abused, and the fact that if I built the right thing, we could save her."

He said he received another call from the Department of Homeland Security, asking if Thorn had the software to track down someone who had been abusing a seven-year-old girl for years and sharing the material over the dark web.

"We were the last line of defence – an actor and his foundation were the potential last line of defence," he said.

Kutcher says Thorn has now come up with the technology to address those issues, thanks to private-public partnerships and the support of Republican Sen. John McCain's charitable foundation.

Kutcher says software produced by Thorn has helped identify more than 6,000 victims of human trafficking, including 2,000 minors, over the last six months, according to data from 25 per cent of users. He says the company's software is now being used by 4,000 law enforcement officials with 900 agencies around the world, and is reducing investigation times by up to 60 per cent.

"Technology can be used to enable slavery, but it can also be used to disable slavery, and that's what we're doing," Kutcher said.

Kutcher urged Congress to sponsor more private-public technology projects that aim to fight child sex trafficking, which is often facilitated through the dark web. He also called for Congress to improve victim support and foster care networks, bolster foreign aid to refugees and pressure corporations to build their products in the United States, rather than using foreign labour trafficking to produce goods on the cheap.

"When people are left out, when they're neglected, when they're not supported and when they're not given the love that they need to grow, it becomes an incubator for trafficking," he said.

Kutcher also said the Syrian refugee crisis must be addressed if the U.S. really wants to be serious about ending slavery.

"We cannot ignore our support for this issue in that space, because otherwise we're going to deal with it for years to come."

Kutcher testified alongside Elisa Massimo, president and CEO of Human Rights First.

The hearing was part of Republican Sen. Bob Corker's End Modern Slavery Initiative, which he launched in February of 2015. The initiative aims to raise billions of dollars to reduce modern slavery in the United States and abroad through bipartisan efforts.