The young woman found naked in a duffel bag and dumped under railroad tracks in East Harlem was a homeless drug addict known in the neighborhood as “sweetie,” a local drug counselor told The Post.

Madelyn Sosa, a recovering addict who now works with the Addiction Institute of Mount Sinai, said she saw the tragic woman just hours before her body was found dumped under Metro-North tracks at 125th Street and Park Avenue around 7 p.m. Monday.

“I called her ‘Sweetie,'” Sosa, 50, said Tuesday. “I saw her [Monday] morning and she was fine when I saw her. But as the day progressed, I heard that she was heavily sedated.

“She’s smoke K2, do heroin, smoke crack, do the pills,” she said. “The lifestyle of the streets: Whatever is available.”

Sosa said she never knew “Sweetie’s” real name, but sa

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