A few parents "cross-the-line" with respect to how/where they engage their children on social websites.

There are some lines that shouldn't be crossed - where the interaction is no longer one-to-one, but one-to-many and the "many" in this scenario are all of your child's friends.    Even though you can create one-to-one interactions in some of these environments, those one-to-one interactions are taking place in a medium that is more oriented towards friend-to-friend vs. parent-to-child.

Facebook, Snapchat, Vine, and Twitter are off limits for father-to-son/daughter exchanges.  These are universes where your kids exchange with their friends.  It is sacred ground.   Keep your distance.

A link on social media that parents might find valuable:

http://www.webmd.com/parenting/features/social-media-and-tweens-teens

And another that parents might find amusing:
http://thefw.com/parents-using-facebook/