The youth team talent was only given a professional contract in February and had not made his debut in Germany's top flight.
"This morning we received the terrible news that our 19-year-old forward lost his life after a car crash in the early hours of this morning," said the club in a statement on their website.
According to police, Feierabend was one of three backseat passengers who suffered fatal injuries when the car they were in left the road and hit a tree at 0545 (0345 GMT) on Sunday morning.
He had played for Hanover 96's youth team in a game against RB Leipzig on Saturday and Hanover's reserve team game on Sunday was called off out of respect for Feierabend's family.
Bottom side Hanover had their relegation from Germany's top flight confirmed on Saturday when they were beaten 3-1 at home by Schalke -- their 22nd defeat in 32 league games.