On April 29 2017 a user in the official #cicadasolvers IRC channel discovered a new/unknown PGP signed message by Cicada 3301. The user themselves said, that he was actually searching an older PGP signed message from Cicada 3301 on pastebin. He used the (there still existing) search function & acutally found a new message. You can read the full story on the uncovering-cicada-Wiki!
Until now, no one knows if Cicada 3301 just placed the message there to be found by someone randomly, or if it was their intention to e.g. post it to their Twitter account or somewhere else.
This is also the last officially confirmed activity by Cicada 3301 which is publicly available and known.