I guess poloniex is good one to try, but better try small amount first then work on it until you know how will your money grow in their hands, also there are some gambling sites that looks for investors yet hard to give trust. But then investing is always together with risk.
I have checked many times, there were plenty of lenders on poloniex whereas there were no borrowers. Because you can only use that only for your margin trading, and only your profits and your original capital will be available for withdraw.
At the same time, we try Bitcointalk lending section as there are people always asking for loans, with the proper collateral the success rate will be relatively huge always.