Hi MikeCOM,
I have checked test server with CentOS7, log files of [Plesk] php7.0-fpm located in directory "/var/log/plesk-php70-fpm/". Plesk-php70 logrotate policy configures in /etc/logrotate.d/plesk-php70.
What OS/version do you use? Who is a vendor of php70-fpm that you use?