Well, today when i logged on. EVERYTHING WAS GONE. I believe that when i was offline, some jerk decided to steal my gold, my items. Im really about to quit on the sever cause nobody likes me. Plus they wont help :l I thought the sever was full of cool people, Not douchebags.
You should lock your chests with /cprivate I would also try and live as far away from spawn as possible, and if you are not already you should apply to become a member and live in the member worlds.
If you don't want to lock a chest, you can use the enderchests at /warp spawn and keep valuables in your inventory when logging out. Also, all of sharq's advice