Bitcoins is itself a investment , Its like a share market price up and down Ever Sec . so its depend on you want to invest bitcoins in following -
Invest in trading area
Invest in Bitcoin Faucet (high investment gives high return Experience need)
Invest in btcjam get Flat Return (invest only in Trusted person)
also you can invest at LOAN in poloniex, also you can give Loan to some people trusted at bitcointalk
high profit

but the problem with using poloniex is that they will ask you for a lot of your personal information
so in order to be able to use their website you have to sacrifice your privacy, and this can be a deal breaker for a lot of people.