You could also invest in a revenue sharing scheme such as [~snip~]. Here if you invest some BTC to buy adshares, you earn 120% back on your investment and can get paid out again by BTC, thus increasing your earnings.
Investment schemes are risky and i think all of them are scammers.. better to stay away from those site if thats investment ponzi schemes..
No investment site are legit so this is not the best to get bitcoin... but this revenue sharing if it is free without investing any but you will earn.. you can try it but make sure that you don't invest..