According to US media, police sources identified the young woman as Alyssa Elsman, who was visiting New York City from Michigan with her family.
The 18-year-old was pronounced dead at the scene, and her 13-year-old sister was taken to a nearby hospital for treatment.
Just moments the incident, Ms Elsman posted a video to Instagram atop New York’s famous red staircase at the Crossroads of the World.
Trevor West, Ms Elsman’s devastated boyfriend, told the New York Post she was on holiday with her mother and friend and that he “knew something horrible happened” when he had not heard from her in a while.
He said: “She would always text me back as quick as she could and when I didn’t hear from her or her friend, I knew something horrible happened. I knew something was wrong.
“She motivated me, loved me, gave me everything I needed that I couldn’t give myself. And now that she’s gone, I don’t know how I’m going to fill that void.
“I don’t know how I’m going to function without her ever again.”
Ms Elsman was killed when Richard Rojas, 26, ploughed a car into her and two dozen others yesterday.
Rojas, who reportedly has a history of offences for driving while intoxicated, was quickly apprehended at the scene.
He was taken into custody and given a breathalyser by officers, which found him not to be under the influence of alcohol.
Law enforcement officials have now said Rojas was likely under the influence of a drug ingested via smoking.