7:04 PM PT -- Jamie's rep tells TMZ ... "All of these allegations are completely unfounded and we believe part of a targeted extortion scheme." The rep claims "Anthony Oliver has a history of filing lawsuits, and has filed 27 federal lawsuits in the past 8 years."

"Melrose Place" star Jamie Luner has been sued for allegedly seducing a 16-year-old boy into a sexual act, and according to the lawsuit he was not her only victim. And ... he's suing for $250 million.

Anthony Oliver claims back in 1998, he attended a house party thrown by Luner to celebrate the success of the show. He ended up at the party because Luner's makeup artist knew Anthony's brother and the makeup artist developed a crush on Anthony.

Anthony says Luner saw him and called him "adorable." He says Luner asked if he wanted a drink, and he said he was only 16 but she had the makeup artist pour Anthony a Jack and coke. They drank and talked for 3 hours, went to her room, and he says she removed a small plastic bag of crystal meth from her purse.

He says she told him, "It's going to make you real horny." He protested using the drug but instead asked for 2 Tylenols, which he says was laced with the crystal meth. His head began spinning and he says he became sexually aroused.

The makeup guy told Luner, who was 26, to go to her room and put on her kitty cat outfit and went to a couch, and he says she began licking his neck, chest and arms and removed his belt, underwear and socks.

He says she performed oral sex on him and took his penis out of her mouth and put it in the mouth of the makeup artist. He claims he ended up having sex with Luner multiple times, and claims she said, "come bend me over the couch and ram me."

And there's this ... the plaintiff's brother had left the party, and when he returned he recorded Anthony and Luner having sex.

Anthony says the experience messed up his life. The lawsuit says, "Plaintiff is left not knowing if he is attracted to men, women or both." He blames the experience for turning him into an alcoholic.

According to the lawsuit, various young men came forward to the LAPD, claiming they were also sexually assaulted by Luner. He says 2 other men accused her of drug-induced sex.

He's suing for sexual battery and emotional distress.

Anthony has already filed a police report.

We've reached out to Luner's rep ... so far, no word back.