If you have a child that is being bullied online, you can take legal action.
Report the bullying as a crime. Tennessee has a law in place to attempt to address this problem, at least to some extent, Tennessee Code 39-17-308.
If the authorities do not take aggressive action call me at (615) 403-2971. Few things make me madder than bullying especially when its done online and in social media, a sad example of which can be found here.