Most of the players are located in the GMT-5 (or so) timezone, which mean that it's quite possible that you won't find much people a monday night at 3:00 AM or simply during the day as most of people are going to school/working/etc.
For now I think during the evening it can go up to 50-60 online players (maybe more if there's an event) and sometimes 80-90 if we're lucky in woe. o_o