Does the school have a police liason officer, employed by the city but at the school? We do. Get to know him/her well. GO to the local police as well.
When you see ANY threats, PRINT the info and keep it. This is your file for evidence.
I am saying this because: my daughter, co captain of cheer, orchestra, honors student has been cyberbullied. I routinely check her facebook and no specific threats are there. HOWEVER, there is a site very popular with teens now because it is anon and kids can send messages without being known. It is called Formspring. It is an EVIL site. Kids post messages to others and some are extremely bad all anon.
My daughter does NOT have a Formspring account. I asked her why...she said because people can ask any question, make any comment and be unknown. It sets you up to be abused. SO, in our case, people have threatened my daughter on her friend's sites of formspring. I check it daily. I print ANYTHING with my daughter's name. The hardest part is the police can do nothing because the actual threat does not come through on our laptops or her phone, HOWEVER they are a clear threat.
While the school said they "could not be a bodyguard" it was ironic that for 4 days, my daughter said every time she walked out of class the police offier was in sight.
We have police reports on file with copies of everything I have printed on facebook and formspring. I have patiently waited on some little biotch to slip up and not hit the anon button. I had a feeling who it was from early on. It is obviously a girl, same language every time. The police agree.
As soon as daughter was named captain and her friend got captain of drill team, it started. The police said...this is part of being captain of the cheer and drill team.
Keep records of EVERYTIME you see something online.
In 1 instance, a girl sent a very ugly threatening message on FB to my daughter supposedly anon but she messed up and daughter got the info and I printed before it was deleted. I proceeded to deliver a copy of what the girl said to my daughter to her parents. The girl is scared of us right now because in a heartbeat, I don't care who you are, I will press charges if you mess with my child.
Take a strong stance. Hang in there and please stand by the side of the child being bullied. My daughter lets it slide. She gets called names but she told me...."mom, I can handle the name calling, I can't handle being called fat (not an ounce of fat on her body) or acne face (flawless skin). She is not called fat or anything like that.
Stay strong. Word is out around here that we are looking for the culprit and I am very involved at the school. The school year just started and an whole new rule has been put in place regarding cyberbully.
Good luck.