The sources said the missile landed by the car as it was travelling just outside the town of Beit Lahiya.
Four people inside the vehicle were wounded, one seriously.
The teenage bystander was killed by flying shrapnel from the strike, Palestinian medical staff said.
The Israeli army said it was unaware of any air strikes in the area but was checking the report.
The Israeli army has killed 154 Palestinians, more than half of them civilians, in Gaza since it began an offensive to stop rockets being fired into Israel and to pressure fighters to free a soldier captured on June 25.
Also on Tuesday, a 13-year-old Palestinian girl died of wounds she sustained when an Israeli tank shell struck her home last week, medics said. Israel had said it had fired at militants who attacked troops in the area.