Sorry for the delay, but until recently Tapatalk has been a pain in my butt. Now they've made it easy, so enjoy it to your heart's content.
The app is currently available free of charge for Android users at GetJar
. $2.99 most other places and for the iPhone/iPad/iPod crowd.
If you're using Chrome, there is also a free "Private Message Notifier" available. It should only let you know once.