SBMFF
I don't know that I agree that you have to know someone in order to stalk them. I had seen a guy on a bike once (long ago, so pre-internet, FB, etc.) downtown (smallish city around 76K population) and he smiled at me. I went about my business and thought nothing of it. A few days later I walked out my door to go to my car and there he was, sitting on his bike for who knows how long, facing my house, and smiled at me when he saw me. I don't know who he was but that felt like stalking to me and it creeped me out and made me VERY uncomfortable. My house was on a quiet street that was out of the way so he was there, facing my house for a reason, and I feel it was because he somehow figured out where I lived by following my car. Or he had ridden up and down several streets, looking for my car which was visible down a long driveway. I can't think of any other way.
So it's my opinion that the early stages of stalking someone can be done without knowing them. You follow someone around who catches your eye to figure out who they are, where they live, work, shop, hang out, etc., and in this day and age you can then continuing your stalking online. There just wasn't the online factor 40+ yrs ago.