how to mass delete messages in imessage?

Than youj so much. saved me tons of time. The people at the Apple Store didn't even know this one.

Happy 2018

To access your user Library so you can try dialabrain's suggestion, go to Finder and select your user/home folder. With that Finder window as the front window, either select Finder/View/Show View options or go command - J. When the View options opens, check ’Show Library Folder’. That should make your user library folder visible in your user/home folder. Select Library.

Yes! Hold down OPTION +COMMAND, then rapidly hit delete. The messages will delete very fast.

You can't.

Perhaps this no longer works but you used to be able to go to ~/Library/Messages and delete chat.db, chat.db-shm and chat.db-wal which would delete all messages.

Thanks Eric. I should have mentioned that but I was feeling lazy.

You are welcome. 😁