If I were you I would just hold these Bitcoins until the end of the year. With block reward halving commencing soon the price of Bitcoin may very well increase on its own and you won't need to participate in any investment schemes in order to gain more money. If you would like to multiply your Bitcoin stash though you should stay away from any HIYP or lending offers and I would recommend looking into trading because I am not trusting other people with my money to earn more money when I can do that myself  Just stay safe and hold some more because I believe the payback will be real after the halving or in 2017 at the latest.