after 6 pages we didn't find any good method for multiply our btc with low risk... 
You can just work to get them, produce something, or exchange something for bitcoins.
but this is not multiply, this is just buying news one... in fact is what I do because I didn't find any better method
And how do you pretend to multiply, unless you are able to "print" bitcoins? If your BTC balance grows is because another one's diminishes. And that happens when you are giving him something in exchange (or stealing him...).