Brooke Hughes, 18, was filming on her phone while driving slowly along Interstate 380 near Tobyhanna, Pennsylvania, just after midnight on Tuesday.
Her passenger, 19-year-old Chaniya Morrison-Toomey, can be heard asking “Are you going live?”
But Ms Hughes did not have time to answer, the Scranton Times-Tribune reports, before lights flash inside the car and screeching tyres are heard.
A tractor trailer had hit the back of their car.
The video reportedly continues for several minutes before a man’s voice is heard and a blurry, bearded face appears in shot.
The car was so badly damaged by flames that it was hard to know what condition it was in before, police said.
Friend Samantha Piasecki, 17, said she had been in the car with the pair earlier in the evening.
She said of her friends: “They were both down-to-earth people. They had good personalities.
“They had smiles that could light up dark rooms. Anytime you were with them it was always fun.”