Can't make writable USB thumbdrive installer anymore

[David Griffith <dave@661.org>]

I used to be able to make a writable USB thumbdrive installer by following 
the directions found at 
https://hyper.to/blog/link/debian-installer-on-a-usb-key/, altering the 
name of the release and device.  Now I can't get it to work.  When I boot 
the resulting thumb drive, I get this:

List of all partitions:
No filesystem could mount root, tried:
Kernel panic - not syncing: VFS: Unable to mount root fs on unknown - 
block (0,0)
Pid: 1, comm: swapper/0 Not tainted 3.2.0-4-amd64 #1 Debian 3.2.78-1

The system I'm using to create the thumb drive is Debian 8.  I've tried to 
make installers for 7 and 8 without success.  I used to be able to make 
viable writable install thumbdrives for Debian 7 and 8.  What happened?

--
David Griffith
dave@661.org