Ms. Majors, a musician and aspiring journalist who had just moved to New York this year for college, was passing through Morningside Park on the way home when she was attacked by at least three young teenagers, the police said. Her killing stunned the city and evoked a bygone era when violent robberies and murders were commonplace.

On Friday night, in an unusual move, the police distributed a photo of the wanted teenager on social media and asked the public for help in finding him. Minutes later, an official police Twitter account said the teenager was wanted in connection with the stabbing in Morningside Park.

The New York Times generally does not publish photos of minors accused of crimes.

The distribution of the photograph was a measure of the difficulty investigators have faced in locating the teenager, whom they identified early on in the investigation but whose whereabouts is still a mystery.

“First and foremost what we want is to bring closure to this case, appropriately, working together hand in hand with the prosecutors,” Dermot F. Shea, the police commissioner, said on Friday, when asked whether any progress had been made in the investigation.