Facebook sign in uses your email or phone number as username when you login. If you don’t remember your email or phone number, you’ll have to try using your username to log in. If you forgot your user name for Facebook sign in, just go ask a friend to look you up on Facebook so you can find it.
A great way to find your email address or phone number is to just ask a friend to look at your profile and tell you your email or phone address and use that to sign in to Facebook. If you are still having trouble signing into Facebook, go to the password reset page where you can go through the process of validating your identity so you can then sign into your account.
The Facebook mobile sign in can be annoying because the app generally takes a long time to load. If you’re having trouble signing into Facebook mobile, simply reset your phone or stop other apps so that you can then sign into your Facebook account.