Years ago I used to accept student friend requests on the Facebook platform, but I came to regret doing that. At some point I stopped accepting student friend requests on social media. 

Steven Krantz in *How to Teach Mathematics* makes the point that you need some amount of social distance from yoyr students to hold their respect, and to not do that is a common mistake for younger/newer faculty. I've certainly walked that path myself. (U.S. system here, maybe that varies by institution and/or country.)