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.
But if we don't have ability to playing Gambling , we will lose many money in gambling.