There are lots of trading sites that you can put in your investment. You can put it in kraken or coinbase or vittrex. These are few of the most trusted trading sites out there. But don't assume your gonna multiply your bitcoin immediately. All investments are risks. Only invest what you're willing to lose.
To me trading is another way a person can easily lose their investments if they are not very careful about the whole thing, I would invest my BTC in my wallet because I know that in due time it value is going to rise and not risk it by trading.