The menacing message was posted in on the gaming forum jeuxvideo.com earlier this week.
In it the anonymous poster, writing under the pseudonym "dead man" said he would write “the last chapter of his life” and that he intended to commit a massacre in a school using his uncle’s gun.
“I live in a certain city, where there is a certain high school, and on Friday I leave my mark in history. My life and the lives of many other people will finish on this day [Friday]” the message read.
The message was posted in an internet café in the city of Strasbourg.
Police have released this photo of the teenager who is suspected of having posted the threat in the hope the public can help track him down.
The threat, which comes a day after a 51-year-old burst into a school in Paris before shooting himself in the head in front of terrified school children, is being taken seriously by police.
Officers have been stationed at several schools across the city on Friday in the case that the anonymous poster carries out his threat.
Around 255 policemen are working around the clock to try to identify the person behind the message.
Police are appealing for witnesses and are asking anyone with information to call 03 90 23 13 05.
Thursday’s shocking incident, which saw a man with a history of family problems commit suicide in front of a dozen young children in the hall of a Catholic primary school in Paris, sparked a debate about security at French schools.
The man, who was not affiliated with the school, forced his way into the La Rochefoucauld primary in central Paris at 11:30 am, pushing aside two adults who tried to stop him, Francois Weil, the city's top educational official said.
On Friday France's Interior Minister Manuel Valls poured cold water on the idea of installing metal detectors at schools across the country, saying it would be "difficult" due to the high number of institutions.
"Can we really stop a desperate man who has decided to end his days in this way? It seems difficult to me, " Valls said.
The Minister said it would not be right to simply react to the public emotion caused by the incident and station, police and metal detectors in all schools.
"That is the case in the United States in particular and look what situation they are in there," Valls said, in reference to the number of school shootings in the America.