Ind. police say there's still hope in the Lauren Spierer investigation

(CBS/AP/WISH) INDIANAPOLIS - Police say they still have hope in the search for missing Indiana University student Lauren Spierer.

When asked at Friday's press briefing if he thought Spierer was still alive, Bloomington police Lt. Bill Parker said, "I believe that she certainly may be, and I hope she certainly is."

Led by an anonymous tip, dive teams searched Lake Monroe using boats and sonar for signs of the missing girl Wednesday and Thursday but failed to turn up any signs of Spierer, police say. 

Over 100 volunteers reportedly searched the 100-acre Griffy Reservoir for clues, but also failed to turn up any information pertaining to Spierer's disappearance.

Canine searches, witness checkpoints, and surveillance videos have also not proved fruitful in finding the missing 20-year-old from suburban New York City.

Spierer, whose disappearance will be featured on America's Most Wanted Saturday, was last seen walking alone toward her Bloomington apartment building around 4:30 a.m. a week ago Friday.

Although police say they do not have anybody that they "characterize as a suspect at this time," investigators say that Spierer's boyfriend is one of the "persons of interest" who they are questioning.

Spierer's family is offering a $100,000 reward for any information leading to the student's safe return, according to CBS affiliate WISH-TV. An additional $45,000 is reportedly being offered by various donors.