He want to invest his BTC on reliable sites. Better don't invest in any ponzi schemes, where they offer very attractive interest but at the end you lose you investment itself.
In this forum there couple of good gambling sites are there, where they accept investment but it also comes with risks because if gambling house lose money than you also will lose you're money. So not 100% safe investment.
You can also lend you're btc with proper collateral, which gives you some interest but don't lend any one without collateral.
If you're thinking of lending why not try out LoanBase? They're strict about loans nowadays, from what I saw in their site a while ago they're not allowing us to choose the loans we invest unto but we can only pick from their investment 'categories.' They'd spread the risk for you according to what you can take.