Are you logging on via Diplomacy? Are you able to access the Lobby chat channel?
Sadly, the game just has low player counts and many of the people who do play only play private comp stomps with their friends. However, there are still games to be had if you log on between, say, 3 pm and 10 pm U.S. Eastern time. The activity has decreased somewhat since the Beta was released because many people who used to play Diplomacy are now spending time on the Beta. Before that there were normally a couple 4v4 and 5v5 games every night.
The problem with this game is that 99% of all Sins players only play offline against AI. If they could all overcome their fears of losing to other people, they could come online at once and have tons of new people to play against.