The Suffolk County Police Department issued a Silver Alert for 17-year-old Melissa DiDaniele, of East Northport, on Wednesday night.
DiDaniele, who has ties to the South Fork, was last seen in Central Park in New York City on Dec. 6, but she left her house on Dec. 2. Police said she may be suffering from bipolar disorder.
"Her family fears she may not be seeking shelter from the cold weather and would like to locate her," police said in a statement.
DiDaniele is described as a white female with short dark hair, blue eyes and a lip ring. She is 5 feet tall and weighs 110 pounds. She was last seen wearing black pants, a green coat, a multi-colored beanie hat and a black backpack. She may or may not be wearing non-prescription glasses that have a black frame.
Detectives have asked anyone with information on her whereabouts to call the Second Squad at 631-854-8252.