"We're looking for any kind of physical evidence to point us in one direction or another. Right now, we don't have anything that says it's an abduction and we don't have anything that says it's not," said Lt. Rich Lawhead of the San Bernardino Police Department.
Investigators are working with Cal State University, San Bernardino police and the San Bernardino County Sheriff's Department in their search.
Barber's laptop and cellphone were discovered in bushes near her apartment under suspicious circumstances.
"The personal items that were found in the bushes are in the bushes, but they're not in there like they were thrown in there," Lawhead said. "They're not in there like they're broken or anything else. It's almost like they were placed there."
Investigators are looking through Barber's laptop and emails in search of any clues. Barber didn't have any social media accounts.
On Tuesday, her parents asked the public for help in locating their daughter.
"I just ask that if anybody has anything, any information that would lead to her safe return, please contact law enforcement as soon as possible," father Stephen Barber said.
Her disappearance is particularly concerning given the recent attacks on women at CSU San Bernardino. On Wednesday, police released a sketch of a suspect wanted in connection to the attacks on campus.
Police would not say whether the case is related to the recent crimes, but all agencies are working together to find the missing woman. Barber lives across the street from the campus but is not a student.
Lawhead says bloodhounds tracked Barber from her apartment door to her apartment complex's front gate, and then the trail went cold. He says it suggests she may have gotten in a car. Police served a search warrant at Barber's apartment Wednesday in search of clues.
"We have really done an extensive search in and around that apartment complex and around Cal State, and that kind of stuff, in an effort to locate any physical evidence," Lawhead said.
Barber's family believes she was wearing the above blouse when she disappeared. She is described as a white female, approximately 5 feet 8 inches tall, 125 pounds, with long red-brown straight hair and green eyes.
Anyone with information is urged to call the San Bernardino Police Department Investigations Bureau at (909) 384-5615.
The Associated Press contributed to this report.