Currently the alert in Sinefa is only available for capacity/throughput/availability/link status related metrics, there is no metric available for what application user is surfing. For more info on setting up alerts – How to Setup Alerting
However, utilization report can be setup to send to customer on a daily basis, which will help customer regularly keep track who is accessing the said websites. Such as report for who is surfing Facebook.
To learn how you can setup schedule reports – How to Setup Report Scheduling