This kind of loan transaction is uncertain,because until now almost all lenders requires proof of properties as collateral including sign of contract so its new which is unfair to other company.
There are companies allowing you to get a loan with cryptocurrency as collateral. Maybe in future we will see companies giving bitcoin loans for fiat deposits as collateral just like the banking system does. People need these loans for trading so there is a market to develop on here.
why not try Margin Trading? You can borrow funds and you can trade more than the amount that you have on your account. It is a different concept but the results were the same. I haven't heard a crypto exchange that offers that kind of services but some wallets like NEXO offers loan services but it needs crypto collateral.
The OP did not respond but I think this was what they were asking for. Leverage trading and margin trading is what was could be made out from the OP. Even then a loan shark's loan to trade is also possible.
But the more secure option for a loan shark would be to ask the borrower to borrow from the broker, that is margin.