According to the article that was posted on the first of November this year, Americans are leaving more expensive parts of the metropolitan areas at a much higher and quicker rate than they are being replaced. This means that there are more empty apartments in these larger cities and the problem doesn't seem to be solving itself. While this is great news for you if you own property in a smaller area, it's certainly not good the closer you get to a large city.
Research states that not everyone is being forced out by their inability to pay the same rent anymore. The problem seems to be that either landlords are raising the rent above what the tenant had been paying or the tenant simply finds a comparable apartment outside of the city limits at a much better price. These are both very valid reasons to move, but that still doesn't help you. If everyone is moving away from where your properties are located, then what are you to do?
The first thing you should do is check around to see what others are charging for rent. If you find an apartment that still has people living there, try and find out what they are paying for the property. This will give you a good idea of where to set your rent at to keep people living there while still turning a profit. If you cannot find anyone that is willing to give you that information, your best bet is most likely to lower what you are asking at least a little. It isn't something you may want to do, but a person in the apartment is better than nothing.
This trend may very well only last a little while, but in the meantime certainly keep an eye on any reports that may be done on this. It never hurts to know what you should be expecting.