The new law paves the way for victims of sex trafficking to hold websites accountable for knowingly facilitating sex trafficking.

"Trafficking is probably worse today than at any time in our history," the President said during the signing ceremony. "You are not alone."

While the problem is chronically underreported and there is no official estimate of the total number of victims in the US, an estimate from advocacy group Polaris puts the number of victims nationally "into the hundreds of thousands when estimates of both adults and minors and sex trafficking and labor trafficking are aggregated."

The legislation received support from members on both sides of the aisle, as well as advocacy organizations like Polaris, ECPAT USA and the National Center on Missing & Exploited Children. Sens. Rob Portman, R-Ohio, and Richard Blumenthal, D-Connecticut, spearheaded the bill's efforts in the Senate. Rep. Ann Wagner, R-Missouri, sponsored the bipartisan House bill.

Even before getting signed, the legislation already had an effect: some sites facilitating sex trafficking have shut down; Reddit has changed its policy "regarding paid services involving physical sexual contact"; Craigslist has shuttered its personal ads section.

"We've already interrupted 87% of the global ad volume. Thirty-plus websites and online platforms have either shut down or had major policy changes," Wagner told CNN in an interview in her office Tuesday afternoon.

The 93-count indictment announced by the Justice Department Monday against seven people associated with major trafficking platform Backpage.com, Wagner said, was a "huge victory" for victims. "Those women and children that have been sold with impunity by Backpage for 15 years."

The new law will build on that, according to the congresswoman.

"This legislation is going to give prosecutors the tools that they need to make sure that no online website, platform, business can ever reach the size and scope of Backpage.com," Wagner said, rattling off a list of other burgeoning sex trafficking sites she's studied over the years: "Escorts in College, Massage Troll, Erotic Review, Night Shift, CityVibe, My Scarlet Book."

Wagner first became involved in anti-trafficking advocacy efforts when she was a US ambassador to Luxembourg. Upon her return to the US at the end of her tenure, she became aware of how pervasive the issue was domestically.

"This wasn't just happening in other countries, it's hiding in plain sight in our own country," she said, noting that in the last five years, there has been an 846% increase in child sex trafficking reports at the same time the crime has moved "from the streets to the Internet."

"People can order up little girls to a hotel room as easy as they could takeout," she said.

The bill has also had a high-profile advocate in first daughter and senior adviser Ivanka Trump, who adopted combating human trafficking as a part of her West Wing portfolio, hosting multiple listening sessions and meetings on the topic in recent months.

The President praised his daughter's efforts during the signing ceremony.

"I have to give credit to Ivanka Trump," Trump said, pointing to his daughter who was standing behind him.

Wagner told CNN the first daughter was "one of the moving forces in this arena."

"This is someone who can raise a level of awareness just by talking about it, by tweeting something out, by bringing legislators together," she said.

Human trafficking is a pervasive humanitarian epidemic both domestically and abroad. Together we are working to combat this critical issue. pic.twitter.com/Py6a89Mcth — Ivanka Trump (@IvankaTrump) May 17, 2017

But an awareness deficit still remains, something Wagner plans to continue to address, which includes partnering with the hospitality industry, visitors bureaus, educators, emergency room nurses and transportation companies, among others.

Most prosecution for sex trafficking offenders happen at the state and local levels, and moving forward, Wagner is working to get a version of FOSTA framework passed in all 50 state legislatures.

"It's hard to do big things. I've passed a lot of bills -- this was hard. And to do hard things, it takes a lot of grit and gumption a little grace from God," she said.