I'm pretty sure ever since upgrading to Yosemite, Facebook and Twitter have been nonexistent in Notification Center. I do recall receiving notifications for Facebook comments and messages and Twitter DMs in Mavericks. I've tried deleting and re-adding the accounts, toggling them on and off in Notification Center, changing notification preferences on the Facebook and Twitter sites, etc. Nothing seems to work. Am I alone here or are they simply broken now?