-Please, no group invites :)
it sort of saves the ones you find. If you started one coop with someone else it would reset them (suggestion: beat campaign on easy, make a 1month account and sign him in and start up the streets, find them all... however that level where you find dare, that might be a trick with an AFK on your team, at least the log isn't in too far).
I actually just checked every spot, watched videos of people finding them so I knew for sure I got the right place and moved on. I probly only needed about three, but needed to check everywhere.