Kelly Nolan, a 22-year-old University of Wisconsin-Whitewater student, hasn't been seen since June 22 when she left some friends during a night out at Madison's bars. A sister talked to her by phone a few hours later but it's not known what they talked about, the Milwaukee Journal Sentinel reported.
"We don't have any evidence of foul play," said Joel DeSpain, a Madison police spokesman.
The 5-foot-6, 125-pound woman has brown eyes and hair, and was last seen wearing a green, sleeveless scooped-neck shirt and blue jeans, police said.
Nolan's mother, Mary Jane Nolan, said police shared with her that made her more optimistic, WISC-TV reported.
"I won't share (the information) at this time based on the advice it could put a slow down on the investigation or turn it to another direction," Mary Jane Nolan said.
A reward fund was being set up to encourage people to come forward if they have any information.