At the very least, they should raise real estate taxes on empty units. This will penalize people for owning several vacation homes, as well as incentivize landlords to lower rates in order to fill the unit.
Difficult to enforce, but send a few people to jail for real estate tax fraud and the rest will fall in line.
I'm not well read in Marxism so I'm probably not qualified to answer this, but the recurring issue with Communism seems to be the same as capitalism, in that it requires people to not be assholes in order to properly function.