By default Plesk install AWStats and WebAlizer at the time of its installation.
Both of these are popular stats applications freely supported with Plesk.
They work great but some times you may find that stats are not updated for few specific days or completely stopped being updated.
In this case you can manually, forcefully update the stats using following commands :
cd %plesk_bin% statistics.exe –process-domains=yourdomain.com
statistics.exe –http-web-statistics –process-domains=yourdomain.com