The online message board features entries praising students involved a disturbance on the Racecourse, near Unity College, reported in the Chronicle & Echo earlier this week.
It also contains numerous messages making abusive and threatening comments about other students.
One concerned mother, who asked not to be named, said: "It's a horrific website.
"I read all sorts of awful things on it.
"As a parent, it is very frustrating and worrying. It needs to be stopped."
Messages put on the site yesterday included teenagers joking about a fracas on Monday evening, in which a mob of about 60 teenagers on the Racecourse surrounded a fight between rival students, forcing police to be called. Many of the messages also appear to fuel hate campaigns against particular students, with a stream of abuse against them.
Sharron Goode, headteacher at Unity College, and Judith Long, her counterpart at Kingsthorpe Community College, both said they did not know of the site, when contacted by the Chron yesterday.
Mrs Goode added: "It is a very sad aspect of modern life. We want to engage children in more healthy activities, not this sort of behaviour."
But Weston Favell school acting headteacher Ray Cackett had heard of the website before.
"Clearly we are worried. It's very difficult to control. If these websites are closed, they just reopen somewhere else.
"Our school has not had any major problems recently. We are keeping an eye on the situation."
Chief Insp Andy Tresias, of Northamptonshire Police, said: "We are aware of this and other similar websites and we do monitor them. There was no warning in advance of the disturbance that happened on Monday afternoon.
"I am sure parents would join us in saying that it is both sad and disturbing that young people become involved in websites like this, and in fighting each other on a scale that they did earlier this week.
"Parents have to ask their children what they are doing when school ends and also monitor their internet use to ensure they don't take part in anti-social activities such as this."
alison.curtis@northantsnews.co.uk