Screenshots of upcoming Facebook messenger for Windows Phone have been posted at WPLVRS Facebook page. Microsoft has announced during MWC that the messenger is coming to Windows Phone soon.
The Facebook messenger Live Tile reveals itself in the first screenshot and the second screenshot show how the messenger chat windows looks like. The email icon in the top status bar of screenshots shows the Windows Phone 8.1 running on the phone. It may indicate that the Facebook messenger may come with Windows Phone 8.1 itself.