Welcome to the forums. What device do you and what themer/launcher app are you using? Can't you drag the FB icon from the app drawer to your home screen?
✖The Facebook icon is a default app: It can Not disappear from the
apps Drawer..the apps drawer is another name to ID the apps
icon located in last-Lower row in the Home-screen, so Tap
on this icon and follow Javier + 420lyfe answer..SeeYa!