creep on

To creep on someone is to watch, follow, or pursue them in a way that feels intrusive or unsettling—behavior that makes the target uncomfortable.

The phrase often describes unwanted romantic attention: That guy at the bar kept creeping on me.

It also applies to covert social media surveillance: I was creeping on my ex's Instagram at 2 AM.

The latter use is sometimes self-deprecating, acknowledging the behavior as slightly obsessive.