I myself gave reasonable offers on property last January (2017) that are unbelievably still empty. They missed a whole year's rent because they wouldn't negotiate a reasonable price.
This artificially inflates the rental market and is causing big problems with regards to housing affordability for the working class.
Why not just tax investment properties after a certain period of having no lease agreement? This will put an economic incentive on investors to make housing more affordable. Either pay tax, or lower your rental expectations to come in line with supply and demand.
I still find it crazy that middle-class workers with good jobs (let's say 10k/ month) cannot reasonably afford their own decent housing in this city.