Human trafficking is so rampant in Fresno, Calif., one police detective claims "every 16-year-old girl" in the city has been approached by sex traffickers.

The statement sheds light on the epidemic of sexual exploitation playing out in the San Joaquin Valley city, which the Fresno Bee is investigating in a six-week series, launched Monday.

In an interview with a vice detective on the Fresno Police Department's nine-person sex trafficking task force, the Bee revealed the startling extent of traffickers' reach.

One vice detective said he's seen sex-trafficking victims "from every high school in Fresno County — and most junior high schools."

"I'd bet every 16-year-old girl in Fresno has received a message that they didn't know was from a recruiter," the detective told the paper, explaining that recruiting is easier than ever with the advent of the internet.

"They're recruited while sitting next to their parents in the living room," he said.

Online advertisements can reach the eyes of thousands of potential victims in minutes, and such ads prove difficult to trace, the report said.

FBI: Almost 'every popular social media site' being used to recruit sex trafficking victims

Once entangled in the web of sex trafficking, the victims – and those running the operation – can be hard to locate. According to the Fresno Bee, traffickers concentrate their rings in cities along Highway 99 "because of the high concentration of hotels nearby."

According to the Central Valley Justice Coalition, Fresno is attractive to traffickers for a handful of other reasons, including its proximity to other human trafficking hubs, like Sacramento, San Francisco and Los Angeles, and its high population of groups particularly vulnerable to exploitation, including migrant workers and foster care youth.

Human trafficking has become a massive operation in California – and a profitable one at that. The Fresno Bee report claims that the sex trade is "now more lucrative than selling drugs for Fresno's violent criminal street gangs."

The Fresno Police Department combats human trafficking with a "three-pronged approach": rescue victims, arrest traffickers and stem demand.

More than 4,400 human trafficking cases have been reported in 2017, according to the Human Trafficking Resource Center, 705 of which were reported in California — the highest number of cases in any state. The Center estimates that at least 40,000 people have been trafficked in the U.S. since 2007.

Michelle Robertson is an SFGATE staff writer. Email her at mrobertson@sfchronicle.com or find her on Twitter at @mrobertsonsf.