I suggest investing on some legit and trusted bitcoin doubler websites. You can find some in this forum which you can trust because many of the users are being paid by them here.
but most sites bitcoin doubler using a ponzi system which means it will not last long.
Growing your bitcoins in a better way is to do gambling where you know, how to play it. and the area where you gambling you must have some knowledge on it. I think this is the best options where my friends are using it too.
Best option for those who will buy some bitcoin. But not if you are just a starting earner. I would recommend staying at this forum and reading a lot about how you will grow your bitcoin so in the near future where you can earn some with signature campaigns you can have the best possible idea on how you will grew it at your own decision.