Suffolk County Police say 17-year old Melissa Didaniele left her home in East Northport on December 2nd.
She was last seen in Central Park on Friday.
Her family says she may be suffering from her bipolar disorder and might not seek shelter from the cold weather.
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 are asking anyone with information on her whereabouts to call the Second Squad at 631-854-8252.