(CNN) -- Bloomington, Indiana, police said Tuesday they have had no breaks in the case of a missing Indiana University student last seen early Friday morning walking barefoot only a few blocks from her apartment, but they have not ruled out the possibility of foul play.
"We certainly do suspect there could have been foul play," Lt. Bill Parker of the Bloomington Police Department said at a news conference Tuesday morning, noting that Lauren Spierer, 20, seemed to have disappeared off a street corner at 4:30 in the morning with no shoes.
Both police and volunteers are conducting searches, combining to cover a broad area in hopes of finding her.
According to Parker, Spierer had gone out with friends to Kilroy's Sports Bar in Bloomington on the night of June 2. Police have video footage that confirms she was at the bar, but she and a friend went back to her apartment building around 2:30 a.m. on June 3. They went inside but did not enter her apartment, and then walked to a building where some other friends lived at 11th and Morton streets.
Around 4:30 a.m., Spierer said she was ready to go home. A friend saw her walk toward the intersection of 11th Street and College Avenue, but police say surveillance cameras at her building do not show her arriving. She has not been seen since.
Parker said Tuesday that police have Spierer's cell phone so they are unable to use that to track her. Her keys also were reportedly found near the block where she was last seen. He said she has a heart condition that requires medication.
Parker did not go into details about the status of the investigation, but he said police do not have any suspects at this time, though the people who were with her that night "of course are persons of interest."
She has a boyfriend and a large circle of friends, he said. Those who were with her Thursday night have been fully cooperative and have allowed searches of their homes and cars.
Police are concentrating canine searches on the downtown Bloomington area where they know Spierer had been. Additional searching by law enforcement officers and volunteers organized by her parents are spreading out from there. Parker said a sergeant is coordinating with the volunteers and providing a law enforcement presence in case anything is found.
The FBI and Indiana State Police also are assisting with the investigation, particularly providing electronic expertise, he said.
Parker said there has been no indication of whether others in the community may be at risk, but he advised that anyone walking alone early in the morning should take precautions.
Robert Spierer, Lauren's father, also made a statement to the media Tuesday. He thanked the hundreds of people who have volunteered to help so far, but said that "there's a lot more we have to do until we find Lauren."
"Lauren is a child ... that is full of life," Spierer said, "always on the go, fun to be with."
He called her a "loving girl" who spoke to her mother every day and noted that her long hair is "pretty striking," though it is possible someone could have altered her appearance if she was taken against her will. She is described as 4-foot-11 and approximately 95 pounds, with blond hair and blue eyes. When she disappeared, she was wearing black stretch pants, a tank top, a loose light-colored shirt and no shoes.
Spierer urged anyone who may have seen Lauren on Thursday night, no matter how casual or insignificant the sighting seemed, to call police. He also said that volunteer searches will be launched three times a day, at 10 a.m., 2 p.m. and 5:30 p.m., and begged anyone who is able to help to join them.
Anybody with information about Lauren Spierer is asked to contact the Bloomington Police Department at 812-339-4477.