Why do I keep getting Facebook messages from someone I’m not friends with? How are they able to send me messages?
When you are involved in a Facebok event, the event administrators can send out private messages to everyone who has been invited even if they are not friends with those people.
If you are getting Facebook messages from a strange person, check your list of events. Look at all of them, the ones which ones you are attending, not attending, responded “maybe” or have not responded to at all. You can be sent private messages by the admins of all the events in your account regardless of your response status.
Click through to each of the events and look at the list of admins. When you find the name of the person who is sending you messages, click the “Remove from My Events” link underneath the event picture.