It was 165 or more during last night's WoE. As for events.. there is no specific number. Because events are held very often for different people from different time zones. But the major event Trial of Heros usually scores 130+ people online. (Last ToH had 60+ participants?)
Edit:
Stop ninja'ing everyone's posts Ayu and go back to GMing on the server -_- grrrr Let us prove heRO has a friendly community, not only GMs.