Hey gang 
I just checked in my own Diablo III account and my Communities were displaying as usual and showed active users in my various groups, so the service itself is functioning… you may be experiencing unique individual issues with connecting to it, though.
For starters, I’d recommend reviewing overall connection troubleshooting, in particular power cycling hardware and renewing your IP and DNS-flushing:
Let us know if issues persist, but best of luck in your adventures 