Law enforcement sources tell TMZ ... officers have tried contacting Bennett several times, but he's gone radio silent. Jimmy was last heard from in September when he sat down for an interview on Italian television, and got skewered by the host over his claims ... especially when he admitted to ejaculating.

We broke the story ... Bennett, who's now 22, vowed to go to the L.A. County Sheriff's Dept. weeks before his TV appearance to file a sexual assault report against Argento.

We're told he never did, though ... nor has he indicated he still wants to.

As you'll recall ... Argento and Bennett had a sexual encounter in a Marina Del Rey hotel room back in 2013. Bennett snapped a photo of the then 37-year-old in bed with him, shirtless, after they allegedly had intercourse.

Argento, however, claims it wasn't consensual because Bennett jumped on her and she was "frozen."

Bennett later threatened legal action over the incident and, in April, Argento settled with him for $380,000 ... which her late boyfriend, Anthony Bourdain, paid.

It's a crime in California for an adult to have sex with a person under 18, and the maximum penalty for statutory rape in a case like this is 3 years in prison. It's a moot point, though ... unless Bennett contacts police.