In addition to reporting to police, you might want to check nearby businesses to see if there are security cameras which may have recorded the thief in action. My bike was stolen on Brattle 2 years ago and there was footage that showed identifying tattoos. Although the police didn't find the guy, I was lucky enough to actually find my bike 3 weeks later dumped in the bike rack in front of the wedge shaped building at Harvard St & Mass Ave, so keep an eye out.