If they don't listen when you tell them directly that what they're doing is creepy, then I'm not sure. Because if they refuse to listen to you, then I feel it's less likely that they don't know, and more likely that they don't care.

you should talk to them, explain exactly how you think they are being creepy and why. some people just need to be woken up and dont even relazie they are being creepy

Find out what measure they have for this is. Challenge that measure. Not the example of creepy behaviour.

First of all, why do I need to convince them? Is it a friend who’s likely to be arrested or find themselves in trouble because of their actions? Are they being creepy towards me or my loved ones? It all depends. Some situations don’t require any convincing because the person will find themselves at the top of my shit list, and I’m going for the jugular (figuratively of course).

Telling them what they're doing is creepy might work. If that doesn't work, then probably what Shannon said.

You should tell them straight up since no one in their life probably ever has