A lot of times, these are fake accounts designed to spread scams. In case it wasn’t already obvious, Facebook is now trying to do their part to warn users about these messages. Now whenever you receive a message from a stranger not part of your friend’s list on Facebook Messenger, you will get a warning that it could either be a scam or an impersonator.
For example when receiving a message from a stranger, Messenger will show you a warning that offers some advice, like refusing requests to send money. For instances where an account that has been created to look like someone you know, Messenger will also warn users that this account appears to be similar to someone you know and that the person you’re chatting with might not actually be your friend.
These tools don’t actually stop the scams or impersonations from happening, but hopefully the additional warnings will give people some pause before they give away personal information or send money to scammers.