NAPLES — Three people were charged Thursday with threatening to shoot up Lake Region High School in a plot that surfaced on Facebook.

A former Lake Region student, MacKenzie M. Dvorak, 18, of Bridgton, was the only adult charged in the case. She was summoned to court on a charge of terrorizing.

A pair of 16-year-old boys from Casco also were charged, each summoned to appear in court on charges of terrorizing.

One of the boys was on probation at the time, police said, and was taken to the Maine Youth Center for violating conditions.

According to the Cumberland County Sheriff’s Office, the assistant principal of Lake Region High School approached a detective about the matter. Assistant Principal Guy Stickney said a teacher at the school had made him aware of threats being made on the social networking site Facebook.

According to police, threats of violence against the school had been made, though no specific time was mentioned.

The threats involved firearms, according to a Sheriff’s Office news release “and the shooting of many people in general terms at the school.”

An investigation was launched at about 10 a.m. By the end of the day, the three suspects had been charged.

The 16-year-olds were not identified because they are juveniles.