Lots of different ethical issues arise from teachers having social media contact with students, just like ethical issues arise when we combine any work environment with social media access. Many of these issues arise from the fact that social media websites provoke a more informal atmosphere and more informal communication than a typical work environment. Everyone feels the ability to speak without social constraints, like etiquette, when using social media or other types of technology such as texting. Lack of social constraints of course leads to several ethical issues.
One issue concerns the fact that it is difficult for employers to supervise content posted on social media. Such supervision especially becomes difficult if teachers, or other sorts of employees, use their own personal social media web pages rather than an employer-supported social media web page (Institute of Business Ethics, Business Ethics Briefing, "The Ethical Challenges of Social Media"). But even when using employer-supported social media web pages, because of the socially relaxed atmosphere of the Internet, it becomes very easy for a usually upright employee of any sort, even a teacher, to post a comment that is not in keeping with the employer's ethics. There have been many cases of employees posting comments on work-related social media websites that are not in keeping the company's work ethic and integrity, resulting in backlash, such as comments posted by a Nestle employee on Nestle's Facebook "Fan Page" in 2011 ("The Ethical Challenges of Social Media"). It's very safe to assume that the relaxed atmosphere of the Internet might even entice teachers to leave unethical comments on social media websites, and such activity is sadly difficult to supervise and prevent, creating an ethical issue.
What's more, if we couple the lack of supervision with the informality of social media, we get a recipe for all kinds of disasters. One possible disaster we open the doors to is teachers contacting students, especially under-aged students, for inappropriate reasons, even sexual reasons. Another disaster we open the doors to is increased chances for cyberbullying, on either the part of the student or even the teacher. Cyberbullying is when someone makes an emotionally distressing comment via any form of electronic device. Cyberbullying would include negative comments, rumors, or even "embarrassing pictures" ("What is Cyberbullying?"). If teachers and students communicated via social media and the teacher gave an assignment or constructive criticism a student didn't like, how easy would it be for the student to respond through cyberbullying?
Finally, another ethical danger social media poses is that it opens the door to bias and judgements. We already know that many employers browse through social media websites as a means of screening employee prospects. In fact, as of 2011, it was revealed that at least 64% of employee recruiters and "human resource professionals" view two or more social media websites as a means of making recruiting and screening decisions. They view pictures and read posts as a means of determining whether or not a prospective employee is a suitable candidate ("The Ethical Challenges of Social Media"). Many agree that such judgements are biased and unethical; however, the practice still remains. So, what would prevent a teacher using a social media website from doing the same thing? A teacher might look through students' pictures and posts to make judgements about students' work ethic. Such judgements would then cloud the teacher's judgements concerning grading and what sort of feedback to give the student, and such judgements would be biased and unfair.