The man found dead and half-naked in a Queens bird sanctuary was lured there with promises of sex — and then slaughtered by members of the vicious MS-13 gang , according to law enforcement sources.

Ian Cruz, 23, of Far Rockaway, was discovered in Bayswater Point State Park last Friday.

Police have arrested four people in the gruesome killing, including an unidentified 13-year-old girl and 15-year-old boy.

Sources said the teenage girl messaged Cruz online and got him to come meet her for a tryst in the woods sometime between Dec. 15 and 16. Instead, a group of four gangbangers — the girl included — pumped four rounds of .22-caliber ammunition into his head.

Investigators believe the foursome used the same femme fatale to ensnare and kill 17-year-old Harold Sermeno — also of Far Rockaway — who was found fatally shot outside the Five Towns Community Center on Tuesday, sources said.

Police believe both men were mistaken for rival gang members, but it is unclear whether they knew the girl was 13, sources said.

Police arrested Yonathan Sanchez, 22, Carlos Guerro, 18, and the two teens on Saturday, charging them with murder and weapons possession.

Elmer Guttierez, 18, was also collared and hit with weapons possession charges, according to an indictment, which says all five were together Wednesday in a Nameoke Street apartment, where cops later found 900 rounds of .22-caliber ammunition, according to a criminal complaint.

The men had been a surly presence in the apartment building for a while, but the girl only started hanging around the apartment about three weeks ago, according to neighbor Matthew Woodard.

“I heard she was heavily involved,” he said. “You don’t expect a 13-year-old kid to be caught up in something like that.”

Jose Mejia, a neighbor of Cruz, said the dead man was an El Salvadoran construction worker who was recently kicked out by his mom for drinking and smoking pot.

“He had problems. A lot of drinking. A lot of marijuana,” Mejia said. “He is always with three or four or five people, but I don’t know what their business was.”

Additional reporting by Shari Logan and Kevin Sheehan