Niantic has announced it will be pushing out a new update that will enable trainers to login to Pokemon GO with their Facebook account.
When this happens, players will be able to link their Trainer Profile to Facebook and Google, and use any of those accounts to login into Pokemon GO. This includes trainers who currently login via their Pokemon Trainer Club account. The option to link your Trainer Profile to Facebook and Google can be found in Pokemon GO’s Settings menu.
Please note this feature will only be available to trainers aged 13 and over, as Facebook doesn’t allow users under the age of 13 to register an account.