The current pre-release of the client ("pioneer" in the version) is only compatible to itself. So you can only play with other testers. Please be aware!
For some reason, the service that provides that feature didn't come back online during the server restart on the 19th. It will require another server restart to get it back up & running, but it's not a critical service, so it will have to wait until the next planned server service, which is unknown atm.
