Northwestern does not have a lot of fans. That is to be expected when you have a private school with 8,000 undergrads that's not a big part of the region's sporting culture. In fact, when putting together an article on Facebook fans, I found that Northwestern has fewer Facebook fans than any other Power Five school. Fewer than Wake Forest, somehow!
That said, the NU administration has said its goal is to turn non-alumni into NU fans, particularly around Chicago and the North Shore. It seems to be working, as season ticket sales have risen, but the Wildcats seem to be particularly in another area: turning famous people who have no business being Northwestern fans into (at least sort of) Northwestern fans.