The treasure hunt (better known as Igel's Treasure Hunt) is a spontaneous event, what happens from time to time. Igel_Son is the founder/initiatior of this event. You will only see a message from the [Broadcast], that you have to visit the website for a new hunt.
When it starts?
Like written above, there will only be an in-game message and a post on the website about it. There will never be something like an invitation with a date and a time.
How to play?
You have to visit the MassiveCraft website and look at the last post (mainly the first post). In this post you will see pictures from chests in wilderness.
Now you have recognize, wheter you know a location of this pictures or not. If you don't know any of the pictures locations, then visit the Dynmap of MassiveCraft. Choose the world, where the current event is and scan the map and compare it wíth the pictures.
When you reached a chest, take the treasure and message igel_son via personal message or leave a comment with the number of the chest you have found.