If they are actually your friends, you have their phone numbers. If not, they aren't.
Be careful conflating "I don't do X" with "no one does X".
If you were, you'd have his imessage / whatsapp. Facebook is a 3rd tier form of communication for a reason.
FB Messenger is just fine. It has the same features as iMessage and WhatsApp, and plenty of folks use it as primary comms.