I posted this about a month ago, but it's probably worthwhile to put it up again.
Proof of claims need to be filed with the bankruptcy court. The address is
Office of the Clerk
United States Bankruptcy Court
Northern District of California
P.O. Box 7341
San Francisco, CA 94120-7341
You should include a cover letter stating the case name (Hashfast Technologies, LLC) and number (14-30725) and requesting that the Clerk file the claim.
I did that almost a month ago. So far no letter response from them and afaik I have no way to find out if I'm on the creditors list or not.