Brothers friend is a peeping tom, what should I do?

I’m a 16-year-old trans guy, and my little brother (13M) constantly has friends over who treat me strangely. Because of it, I barely leave my room anymore and usually keep my door locked whenever I can. However, something happened last night that has made me feel unsafe even in my own room.

I was alone in my room late at night, doing something most teenagers do when they have privacy. I’d been there for around 30 minutes to an hour when I suddenly heard knocking on my window. When I looked up, I saw a kid standing outside staring directly at me.

Before anyone asks, yes, I had my curtains closed. The problem is that I only have one curtain, and it’s slightly too small to fully cover the window. I’ve been asking my parents for new curtains for a while, but it keeps getting forgotten.

I’m almost certain it was one of my brother’s friends. He had a buzz cut with bleached hair, which isn’t much to go on because my brother and around fifteen other boys all bleached and buzzed their hair together recently. I have no idea which one it was.

The whole situation has left me completely shaken. I don’t feel safe or comfortable in my own room anymore. Part of me wants to find out who did it, but I also have no idea how I’m supposed to approach a group of 13-year-old boys and ask which one was watching me masturbate through my window.

I told my mom about it, and she said it was probably just one of them messing around. Maybe that’s true, but it doesn’t change how violated and unsafe I feel. Someone was outside my window in the middle of the night watching me in what should have been a private space. Since then, I haven’t been able to stop thinking about it, and I honestly don’t know what to do.