FIND HIDDEN UNREAD MESSAGES
Not many people know this but you might be getting messages from people and don't know it. If someone sends you a message and you have no mutual friends, Facebook automatically filters their message into the "Other" message folder.
To find the "Other" folder, click the word bubble icon at the top of the page. Then next to where it says "Inbox" click "Other." Click here to see this in action.
You might see a surprising amount of messages piled up in here, because Facebook never notifies you about any messages received from people who aren't in your network.
In fact, when I originally told my listeners this tip, one girl tried it found a message her birth mother had sent her a few years before. Who knows what you'll find!