Bukkit

Question:
Does this plugin make so you see when someone find diamonds, like it displays for OP's when a player find iron,gold,diamond, I thought it should works, how to do it?

Have you checked the FAQ page?
Yes!

while it does not announce it Hawk eye does log all the diamond ores broken (and diamonds pickup up) you can use for example (if you have the permission) "/hawk search a:block-break f:56 t:1d p:joe_player" to find all the diamond ores that joe_player broke in the last day. you do not need a player name but i do recommend using the t: field (t: =time, h=hour, d=days) or you will get all diamond ores broke since hawkeye started logging.

type "/hawk help search" in-game if you are looking for more things that you can search