I was going to refute your (uncited) comment, but it appears that San Francisco's vacancy rate has increased from 4.9% to 8.3% over ten years, affirming your position.
There's really no citation available so to speak for my comment, unless you want citations in Economics texts. It's fairly rational activity by landlords (or anyone who has controlled supply of any good/service) to take. The vacancy rates aren't surprising to me but there are other effects that cause that number to rise/fall, not just rent control (though the arrow is in the expected direction based on policy).
It's unclear from those stats the reason for the vacancies, though. I've read about a lot of foreign investment that is buying up properties and then intentionally leaving them vacant, or are using them as vacation homes or vacation rentals.