Operation H.O.O.K. (Hands Off Our Kids) busted 19 would-be sex predators last week.
For hours, detectives posed as minors on a variety of online chat rooms and apps.
"All of the suspects were first to express their sexual desires and they initiated a time to meet with a detective posing as a child," said Sheriff Margaret Mims.
Mims said the detectives made clear their fictitious age -- some posing as children as young as 12 -- and still, the men planned to meet with them for sex.
"The greatest evil and the greatest threat to children is the cell phone. This is how children are exploited, this is how they are violated and this is how these predators get access to our children," said Lisa Smittcamp, Fresno County District Attorney.
One of the men arrested, 38-year-old Mark McGill Junior, is a U.S. Forest Service employee.
He showed up to the meeting site in a department fire engine with the intent to have sex with an underage girl.
McGill has bonded out after posting $30,000 bail. Twelve others have also bonded out.
"I want to remind parents that the suspects in these cases may not fit a certain stereotype or profile that you have in mind," said Sheriff Mims.
She said for the 19 captured in this operation, there are thousands of other sex predators out there preying on vulnerable children.
It's important to be aware of what kids are doing, especially as more of them have electronic devices and access to the internet.
Fresno Unified School District shared a list with Action News of apps commonly used by sex predators.