King County sheriff's Sgt. Cindi West said the driver who hit the woman did not stop and remains at large.
The woman, who has yet to be identified, had been in a car with a group of people who left the Snoqualmie Casino at about 3 a.m.
West said the group got into an argument and stopped near 394 Place SE north of North Bend Way, where the woman and the driver got out of the car and walked off in different directions.
The driver eventually went back to the car and the group drove around looking for the woman. They found her body a short time later in a ditch near in the 10200 block of 394 Place SE.
Neighbor Cody Fisher didn't hear or see the fatal crash, but called the narrow, two lane road without shoulders "the raceway." He said it was only a matter of time before someone hit a pedestrian.
"We have high school kids speeding down," Fisher said.
West said detectives searching the scene found pieces of a left front headlight from a full-size pickup truck. Another neighbor said she saw a diesel pickup going up and down the street at 3 a.m.
Tim Noonan lives in the neighborhood and had just returned home when the woman was hit and killed.
"Terrible things can happen in the blink of an eye, and somewhere out there today is someone carrying a lot of pain I'm sure," he said.
Detectives are asking for the public's help locating the driver and said the truck likely has significant damage front-end damage. Anyone with information is asked to call the King County Sheriff's Office at 206-296-3311.
The name of the woman who was killed has not been released, but West said the group of people she was with are all from the North Bend area.