[JohnFen]

Please don't try to scare them. That tactic is very often counterproductive.

Educating them in a factual way that doesn't appeal to their emotions is a better tactic, in my opinion. Perhaps a research project where they actively find all the publicly available data on themselves that they can, combined with lessons about the impact of data leakage on regular people would be sufficient? I don't know.

In the end, teenagers (like everyone else) will make their own decisions about these things. Even if they make decisions that you and I consider foolish, they have the right to decide for themselves. You job is just to ensure that they have the information and understanding they need to make informed decisions, not to evangelize a particular stance.