Where are the proftpd logs located?
I use Centos 6, Apache with virtualmin
You can find those in the "/var/log/proftpd" directory.
I checked in that directory already nothing is contained inside see here > http://puu.sh/8WMpt/81c77d754e.png
and i checked the logging options in virtualmin which is all default > http://puu.sh/8WMtD/61de4d290f.png