Add more VSFTPD virtual user accounts
How to add more virtual user accounts to your VSFTPD on linux.
If you have already set everything up you only need to do this:
sudo htpasswd -d /etc/vsftpd/ftpd.passwd ftpuser
Then you can create their directories:
mkdir /var/www/ftpuser
chmod -w /var/www/ftpuser
mkdir www/ftpuser/www
chmod -R 755 /var/www/ftpuser/www
chown -R vsftpd:nogroup /var/www/ftpuser
And restart the service.
sudo service vsftpd restart