The comedian said she was “p***ed off” because the teen and her cousin Lily had been harassed “everywhere they went” by “grown men” in the capital on a day out.
Recalling the incidents in the latest episode of her podcast, Telling Everybody Everything, she began: “They’ve been out in the day; they’ve been out on the train just doing very wholesome activities.
“Shopping, going to a theme park, doing this and that. And everywhere they go, every day, they have been sexually harassed by grown men.
“Violet is 14, her cousin is 16, but the 16-year-old doesn’t look 25. She looks 16, 17,” she continued.
“There’s no mistaking Violet’s age. She’s 14, she has braces on her teeth. Anyone looking at these girls, no one is mistaking them for being adult women.
“Maybe someone might hope that Lily’s 18, nevertheless, you’re a sick freak and you shouldn’t be chatting to teenage girls the way you are.”
The TV star then explained that while she didn’t want to go into detail about the interactions, she wanted listeners to be aware of what is happening.
She added: “I won’t go into all the incidents because I want to talk about Violet less and less publicly because I do think she’s entitled to privacy, but I’ll only tell you the bits she put on her own Snapchat because she’s posted that now, it’s for public consumption.”
Detailing one incident, Ryan said man started filming the teens while they travelled on the London Underground.
She recalled: “There was a man in the middle of the day filming them on the underground. Just a man on his own who got his phone out and started filming these girls sat opposite them.”
Going on to share another, the Netflix star said the pair went into a shop in Camden where an employee came out from behind the counter and put his arm around Lily then asked her age.
The comedian said: “She says, ‘I’m 16,’ and he asks how long she’s in town for and tries to put his number in her phone.”
Sharing her outrage, Ryan continued: “These men are trying to put me in jail because they better hope I won’t be around [next time]. I’ve been training for this my whole life.
“I’m seeing it now in real-time with a teenager and I don’t know exactly how to handle it,” she said, adding that she found it “very, very scary”.
The Duchess star also admitted that while she often publicly criticises older celebrities for dating younger women, she takes issue with grown men harassing and trying to “chat up” underage girls very seriously.
She concluded: “All my little playful jokes about Leonard DiCaprio – that’s for fun. That’s me taking down a very, very high status 50-year-old celebrity for dating models above the age of 18, but I still think it’s gross.”