Investigators are calling her disappearance suspicious and her family is fearing the worst.
Her friends have scoured the internet looking for signs of the missing home health care worker.
They are passing out fliers with her picture on it, but so far nothing.
"She's not just my baby, she's my best friend," her mother, Barbara Ross, said.
Becky and some friends went to a bar last Thursday night. Nicole Longo left early, but Becky stayed behind.
"She came outside. She grabbed a cigarette and jacket out of my car, and I have not seen her since," Longo said.
Becky then went to another bar with a friend and didn't get home until almost 3:30 Friday morning.
At 6:20, when her alarm clock rang, Becky was gone.
"I looked outside. Her car was there. I started calling her. 'Becky, where are you?'" explained her step-father Larry Ross.
"We have about a two and a half hour window in which she vanished," said Lt. Det. Joseph Williams.
Becky Koster is 5'5" tall, 112 pounds with brown hair and brown eyes. She has piercings on her nose and tongue.
Her mother says she has never disappeared before.
"There isn't a day that goes by that she wouldn't call. If she and I had a disagreement, she would call her friends. There isn't somebody who she wouldn't call. That phone is stuck to her ear," said Ross.