How can you get revenge on a little asshole on the internet?

A bit of background (sorry in advance, I'm writing through a translator).

I am 16, and my friend Saya is 14. We get along well, have many common interests, and support each other. She really values my attitude toward her, and this isn't the first time I've helped her through tough situations—one of which this story is about.

Yesterday, as usual, we were minding our own business, playing games, and drinking tea. Suddenly, her phone started blowing up with messages from her former online friend, with whom she hasn’t spoken for over a year. When she opened the messages, she saw that his friend had also written to her. Apparently, they thought it would be funny to prank her after all this time by sending her old photos with inappropriate drawings on them.

When I saw this, I was boiling with anger. I couldn’t allow this little jerk to torment her again. Over a year ago, something similar but much more serious happened. He threatened to leak her phone number and treated her like some kind of animal. He also sent her tons of 18+ content, which was so disgusting that even I couldn’t bear to look at it.

She liked talking to him, and I didn’t really stop her, but at some point, something clicked in him—probably puberty. I convinced her back then to cut all ties with him and block him everywhere, which she reluctantly did. He was a close friend to her (at least, that’s what she thought), but it all turned out like this.

This idiot kept trying to contact her through different accounts, blackmailing her with messages like, “You won’t get away with this so easily.” But she managed to block him everywhere—until now.

So back to the current situation: He and his friend were sending her those photos on WhatsApp, writing under them, “Did you think I’d forget about you?” Then, about five minutes later, she showed me that her Telegram account was being threatened with deletion.

What does he think he’s doing? When I texted him on her behalf, asking, “What the hell are you doing?” he responded, “Don’t you like the photos? Should I leak them online? It’ll be really, really fun. And if I add your phone number, it’ll be even funnier.”

I couldn’t believe my eyes. I sat there for a minute with mixed emotions—somewhere between anger, frustration, and a deep hatred. If I could, I would have thrown the phone against the wall. Saya didn’t understand what happened, took the phone from my hands, and stood there in shock for a minute.

Unlike me, she started to cry. She already has so many problems, and now this blackmail on top of everything. I hugged her, trying to calm her down, telling her that I would do something about him. I couldn’t sleep all night, thinking only about one thing—what should I do?

I know which city he lives in, but I’m definitely not going to travel 500 km to find him. Should I go to the police? I’m a bit afraid that I might end up in danger because of this “joke.”

I truly feel lost and powerless. I’ve been thinking for a long time about what to do to teach this jerk a lesson—that the internet is not a toy.

In the morning, when Saya woke up and saw me in the same mood as yesterday, she said, “I know what might calm you down.” At first, I thought it would be something obvious, like calmly drinking tea or going for a walk, but no. She showed me that she had some useful information about him on her phone—his name, surname, phone number, and full home address.

When I asked, “Where did you get this?” she said that he had sent her a package a long time ago, and she still had his contact details. I felt a weight lift off my shoulders, but a new question popped up in my head: “What can I do with this information?” And I started overthinking again.

All my thoughts were only about this, and I still haven’t figured anything out. Now I’m writing this post in the hope that someone—anyone—might know how to teach him a lesson. I’ve been on Reddit for a long time, and I know there are some pretty smart people here, so I really hope for your help.