If you have a customer service team, you’ve got a handy list of customers you can apologise to.
If you haven’t got a customer service team, rummage through your inbox and find some people who have written in.
Now, by way of apology, send them an invite to become one of the first members of your new online community. Perhaps give them VIP status. If they have stuck by you, they’ve earned it.
It shows you still care about them. I’m also willing to bet you’ve just recruited a vocal group of participators.