Police said more than 40 investigators are searching by ground, air and water for Keller.
"We're continuing to search the river, continuing to search bodies of water, not so much looking for Toni Keller herself, but any clue [that] would come up," said DeKalb Fire Chief Bruce Harrison.
"At different parts of the area which is approximately 150 acres, it's very dense in areas. It also has the river flowing through it," said Chief Bill Feithen of the DeKalb Police Department.
Members of the NIU community are also helping out.
"I don't need to know her personally. I remember being a freshman here and we need to come together and bring her home," said Jillian Thomas of Huskies United.
Many students are passing out flyers. They've also created a facebook page.
"We just break it down with a grid and going door-to-door and some people don't even know there is anyone missing," said NIU alumna Tania Cervantes.
Campus counselors are reaching out the NIU community.
"The counselors are going to the students and talking to them and talking to faculty and to university personnel here because this affects everybody," said NIU Spokesperson Brad Hoey.
Anyone with information on the teenager's whereabouts is asked to call the DeKalb Major County Case Squad at 815-753-TIPS or 815-748-8407.