Parents from top-tier Forest Hills HS in Queens were horrified to discover the students’ dark secret Wednesday — a catty, cruel Facebook “confession” page that reads like “Mean Girls” meet “Gossip Girl.”

More than 4,100 anonymous posts have gone up in just two months, singling out girls who have “the fattest a– ever,” which kids are having sex and even thoughts of suicide.

“It could lead to bullying or something worse. The administration needs to get involved and do something about it,” said Vic Singh, the parent of a senior.

“It creates an unhealthy school atmosphere,” he added.

Parents found the gossip-fest Wednesday after someone posted a threat reading:

“Don’t come to school tomorrow because something big is going to happen. Seriously, don’t come to school unless you want to be in the news.”

Police found nothing suspicious but parents were almost as disturbed by the Web page itself — which reads like a real-life “Burn Book” from the movie “Mean Girls.”

“Honestly, fat girls need to stop wearing crop tops because i dont want to see any muffin tops or rolls,” one teen griped.

Another student posted,“To all the [rich] girls that complain and push people in the hallways . . . you aren’t some royal highnesses.”

Other teens channeled their inner “Gossip Girl,” professing crushes and baring salacious ­secrets.

“Confession #3919: I just want to lose my virginity already,” one teen posted.

Another added, “Confession #4062: I had to pee and the bathroom was locked, so I pissed in the teachers staircase.”

In one disturbing post, a student described an apparent suicide fantasy.

“Confession #4092: I wanna jump in front of a car like I almost did that one time. Woo. Yeah, f–k my sanity I’m so done right now,” it notes.

Parents now want the school to monitor the Web page to make sure posts don’t spiral out of hand.

“The school should know about the page and do something to monitor it,” said Gary Weil of the school’s Parents Association.

“Kids can be mean-spirited. Some kids enjoy knocking each other down — but you have to take everything like this seriously,” he said.

Principal Saul Gootnick declined to comment.

Department of Education spokeswoman Marge Feinberg said only, “This is a police matter.”