First decide if it should be reported. For that, check When to get help.
Next, make sure you have all the information you need, no matter how you will be reporting it. InternetSuperHeroes.org has some valuable articles on what you'll need if you are reporting cyberabuses. You'll need digital copies of the bullying communications, not just a printout. You'll need to record the header information on any e-mail, and grab the IP address of any other communications. (They can help you with that at WiredSafety.org. Click on their cyberstalking and harassment report link.)
The easy way is to use a monitoring software product (I like Spectorsoft.) that will do the work for you and can be used to provide evidence for law enforcement and legal action.
You have several options when reporting a netbullying problem. You can report it ot the other parents (if you know who the netbully is). You can get the school involved. You can report it to the ISP or hosting company of the netbully or the offending website. You can hire a lawyer and you can call the police.
No matter which tactic you take, you'll need to have all the information. What websites are involved? How long has this been going on? How long have you known about it? How has it affected your child? Have there been offline bullying or communications as well? Are others involved or does it appear ot be a lone netbully? Is it getting worse? Does it involved offline contact information being posted online to the public? What e-mail and instant messaging accounts and screen names are used? If your child's password has been taken, did they share it voluntarily, was it easy to guess or was the account hacked? What actions have you or your child taken to stop it, block it or otherwsie avoid it? Does your child, or do you, know the identity of the netbully? Suspect someone in particular? Why? Did your child provoke it in any way you can determine? Are there sexual harassment issues involved with the netbullying? Are sexual images involved? If so, are the real or created by the netbully?
Pull together a packet and save all communications on your computer in a special file. (Spectorsoft will do this on its own.)
We're working on a report form for netbullying to make it easy for parents. Check back over the next month or so.
If you need help, or have any questions, reach out to us at WiredSafety.org, at our cyberstalking and harassment reportline. We're all unpaid volunteers who want to help.