Anonymous FTP users can't view files

FTP is a very old and very insecure system, you would be much better off using SFTP instead which is supported by Apple's server software.

If you really have to use FTP and really have to use anonymous FTP then it is possible but you have to do several extra steps because as standard Apple deliberately disable anonymous access because of these valid security concerns.

1. Start off with the FTP service turned off
2. Run Server.app and turn on show System Accounts in the View menu
3. In Server.app go to Users and view local accounts and find the FTP Daemon account
4. Edit the 'Access to Services…' via the cog-wheel for the FTP Daemon account and enable FTP access - it sounds like you may have done this already
5. In the FTP Server option in Server.app give 'everyone' read only access, this will allow 'guest' aka 'anonymous' to also read the list of files
6. Using Terminal.app edit the /Library/Server/FTP/Config/ftpd.conf file (you may need to experiment but something like the following would be a starting point)
7. Now turn the FTP service on

# the FTP document for OS X Server users

chroot real /Users/Shared/ftp-root

# match umask from Mac OS X Server ftpd

umask all 022

chroot GUEST /Users/Shared/ftp-root

modify guest on

upload guest off

#disable homedirs

homedir all /

Note: You will probably find that having a space in the chroot path will cause problems, however as you indicate it is currently working for authenticated users this probably does not apply to you.