I would not recommend communicating with a student via email, social networking, or texting.  Middle school especially is a very tenuous age with many hormones and emotions exploding.  We have a strict policy in our district that we can not do any of the above.  The dangers and pitfalls are miscommunication.  We may think we are helping a student when we are questioned about relationships, their parents etc.  If you write something it can come back to haunt you as we have seen on the news.  If you had a class site where the teacher monitored the site regarding a topic you may be studying or how to use social networking appropriately it may be a positive.