Well, I am not that fond of such alerts.
There are a number of outcomes I don't like.
a) those without the media (i.e. twitter) won't get the alert
b) if you miss out for 8h (game day) if you i.e. slept, you will be disappointed
c) if it is a false alert, you basically have a moral right to get it if you were on because of the alert
d) ...
For events in advance, any media will do. I can always also announce ingame.
However, for Kyuubi, it's a bit different, way shorter in terms of time.