By Dan Whitcomb

LOS ANGELES, April 11 (Reuters) - In the year since U.S. authorities shut down sex ad website Backpage.com, the online prostitution market has splintered across a dark and volatile internet landscape with dozens of players trying to fill the void, according to an analysis conducted by a counter-human trafficking technology company.

The report, shared with Reuters by Childsafe.AI, also shows that a landmark package of sex trafficking laws passed by U.S.

Congress, known collectively as SESTA-FOSTA, has made it difficult for sex classified websites to operate.

Instead, the report prepared for use by law enforcement agencies showed the illicit trade of sex trafficking and prostitution of adults and children has begun to shift toward so-called hobby boards and "sugar daddy" pages.

Rob Spectre, CEO of Childsafe.AI, told Reuters in an interview that even as ad levels have begun to rebound, demand remains lower as sex trafficking has become more difficult and less profitable on the internet.

"Basically the ads are back but the buyers aren't," Spectre said.

A recent review of sex web site ad sites showed men complaining to each other about the about higher prices and the difficulty in finding legitimate providers. Some openly lament the absence of Backpage.

Backpage and its affiliate websites were seized on April 6, 2018 in a U.S. Justice Department sex trafficking and child prostitution investigation. Seven people, including the website's founders, were charged in a 93-count indictment with facilitating prostitution, money laundering and fraud.

Days after the Backpage seizure, President Donald Trump signed into law the Stop Enabling Sex Traffickers Act and Fight Online Sex Trafficking Act, or SESTA-FOSTA.

The new laws amended the "safe harbors" provisions of the Communications Decency Act that had protected websites from criminal liability over third-party or user-generated content.

BACKPAGE A 'FULL MONOPOLY'

Sex worker advocates have fiercely criticized SESTA-FOSTA, arguing that taking down Backpage would drive prostitution further underground or into the streets. Free speech activists say the laws unconstitutionally burdens website owners with policing content.

The Childsafe.AI study found that Backpage's closure dealt a huge blow to the illicit world of online prostitution.

Demand for prostitutes dropped 67 percent and search volume plunged 90 percent immediately after the site went offline, the report showed.

While many sex classified websites, mostly run by small-time operators, have tried to fill the gap left by Backpage's demise, they each only draw about 5-8 percent of the unique visitors Backpage was earning at its height in 2016, Spectre said.

In a 2017 U.S. Senate subcommittee report, Senator Claire McCaskill described Backpage as a $600 million company "built on selling sex and, importantly, on selling sex with children."

"I don't think we had any understanding of how dominant Backpage was at the time," Specter said.

"They were a full monopoly on (internet-based) commercial sex in the United States."

"The competition is so fierce, and it's really dirty, to the degree that I'm not sure there's ever going to be a single dominant player ever again," he said.