Airbnb Primary Residence by-law

Does anyone know how to report someone for renting their home through airbnb? The new by-law states that the rental has to be your primary residence and I know for a fact that the owner has not lived there in at least 5 years. I contacted Airbnb but, as expected, they wouldn't do anything as the owner has provided the necessary forms and paid the fee required to rent out their home. I'm tired of people skating by these half measures put in place by the city. Any help would be appreciated.