I don't make any real effort to monitor my kids' activity, because I've seen enough evidence (finding open browser windows, "following" or friending them from my own account, eg.) that they know how to behave, and I trust them. But ... they've grown up in a family that talks a fair bit about all this stuff. Not via parental mini-lectures. More like casual dinner-table conversation about things we've seen on-line, stupid behaviour we've witnessed, things we've discovered about memes and click-jacking and click-baiting, inappropriate posts we've seen from friends and acquaintances, trashy websites, and so on. Often it'll start with someone saying "Oh yeah, and I read on-line that ..." and someone else asking what website it was, and offering a critique of that site's content, and someone else mentioning something really suspect they saw there, and another kid commenting that her classmate is constantly sharing photos from that site, and how she doesn't think that's appropriate, and then there's a discussion about people lacking critical thinking skills, and how easy it is to make judgements about others' intelligence and values and beliefs based on what they share on-line and ...
Anyway, I think a family that talks freely and discerningly about the on-line world will tend to produce kids who are aware of the issues and know how to avoid problems. I admit I will occasionally glance through a logged-in browser window to see what my kids (the under-sixteens, anyway) have been up to, just to reassure myself that there aren't any glaring issues. So far so good. I have four kids, from 11 to 20, all very savvy with social media.
Miranda