Where is your line with students on social media?
My line:
On the first day of classes I tell the students that I don't want to be contacted by social media or by any means other than the school e-mail. The school also gives students a nice way to provide anonymized feedback, which no one has ever used so far.
If students send me friend requests on Facebook et al (which I don't really use), I delete the requests (it's happened a few times).
If students send me friend requests on LinkedIn anyway, I accept the requests after the end of the semester. (I can imagine a scenario where I might want to delete the request, but it hasn't happened yet.)
On at least 4 occasions I remember, former students messaged me via LinkedIn about recommendation letters for graduate school, advice regarding internships, etc. I don't know, maybe they don't have access to school e-mail anymore. I'm a little ambivalent, but so far nothing bad has happened.
I have no doubt that some students create class-related social media discussion groups. I also trust that if something happens that needs my attention (e.g. many people not understanding the material), they will contact me by school e-mail or make an appointment for office hours.