Jose in attention to your post this is the output of the post-install script :

bash-4.3# sh /usr/ports/xfce/elementary-xfce-icon-theme/post-install
gtk-update-icon-cache: No theme index file.
gtk-update-icon-cache: No theme index file.
bash-4.3#

I can still use the tango-icon but when I use the xfce4-appearance-settings to select the elementary-xfce-dark its content seems to be missing. tried to find a repository did not find