Kutcher, 39, co-founded the organisation Thorn: Digital Defenders of Children, which builds software to fight human trafficking.
The "Spotlight" tool, which Kutcher said has helped identify 6,000 victims in six months, was created after a 2012 sex trafficking survey found that 63 percent of underage victims reported being bought or sold online.
The visibly emotional actor - who has two young children with actress Mila Kunis - said: "I've been on FBI raids where I've seen things that no person should ever see.
"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.
"And this child was so conditioned by her environment that she thought she was engaging in play."
Kutcher said his team received a call from the Department of Homeland Security asking for help to find a seven-year-old girl after footage of her being sexually abused was "spread around the dark web".
"She'd been abused for three years and they'd watched her for three years and they could not find the perpetrator, asking us for help," he said.
"We were the last line of defence. An actor and his foundation were the potential last line of defence.
"That's my day job and I'm sticking to it."
Kutcher's comments to the committee follows heightened scrutiny of classified advertising websites such as Backpage.com for carrying ads that offer children for commercial sex.
"Technology can be used to enable slavery, but it can also be used to disable slavery," said Kutcher.
300,000 American children at risk every year
Each year, up to 300,000 children are at risk of being trafficked for commercial sex in the United States, according to the U.S. Department of Justice.
Most sex trafficking victims are advertised or sold online, according to a US senate subcommittee report that was released last month.
Backpage.com was hit last week with the latest in a string of lawsuits that accuse the company of promoting sex trafficking by running and rewriting ads that offer children for commercial sex.
In a more light-hearted moment at the hearing, Kutcher blew a kiss towards Republican senator and former US presidential candidate John McCain.
It came after McCain told the actor: "Ashton, you were better looking in the movies."
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