Where is vsftpd.conf?

You've a weird issue, try clearing you cache, update your repository information and install it again:

sudo apt-get clean
sudo apt-get update
sudo apt-get install --reinstall vsftpd

If this did not work, purge vsftpd (remove it including its configuration files) and reinstall it:

sudo apt-get purge vsftpd
sudo apt-get install vsftpd

It sounds like the installation didn't complete successfully. The quickest solution is probably going to be to reinstall vsftpd:

sudo apt-get install --reinstall vsftpd

Late to the party bu hope what I discovered is useful.

The file is not there after install. However

/etc/vstftd.conf

will be created after starting up the server.
It's installed with

sudo apt-get install vsftpd

and started with

sudo systemctl start vsftpd.service

This should do the job.

Try:

cat /etc/vsftpd/vsftpd.conf

That is where it is located for me.

I had this problem too. When I observed the installation log carefully, it turned out that the installation was stopping before re-installing the directory "srv/ftp". I deleted the directory ftp from /srv so that /srv was empty. Then I reinstalled and had my original vsftpd.conf script replaced in /etc/vsftpd.conf.

Try

sudo dpkg-reconfigure vsftpd

This will affect package's configuration and rerun some scripts designed for package proper operation.

try this command :

sudo find . -type f -name vsftpd.conf|grep vsftpd.conf

it should find the file in ./etc/

if the file is not there, then try following command :

sudo apt-get install --reinstall vsftpd

and then the find again -

If you cannot find the vsftpd.conf under /etc/vstftd.conf, then you need to start vsftpd at least once. This will create the config file afterwards

sudo systemctl start vsftpd.service
ls -lahG /etc