Gloucester County Prosecutor Sean Dalton said Friday that the threats were considered unfounded but that his investigators were looking into the online postings, which came from several Facebook accounts.
The Philadelphia Inquirer reports the threats were coming from a user with the name David Prezet. Students told the newspaper that "Prezet" threatened to "blast everyone in the school." No student by that name attends the school.
The threats were reported Tuesday. Police were at the school to greet students on Wednesday.
Facebook spokeswoman Nicky Jackson Colaco confirmed that the company had received the subpoena. She said users are prohibited from posting threatening content, but declined to comment further.