After watching this video by IGN about raids, I was left with the impression that you need 6 people to do a raid. If Deej or anyone else could clear this up it would be greatly appreciated.
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The answer is no. It says 1-6 players It does not require you to play with only friends either. You can go up to someone randomly and ask if they want to do the raid with you. They do not need to be in your friends list nor in your clan.