So I have a friend putting his Crypto into Nexo.io and I am 100% sure these are scammers as well, promising of up to 20% yields per annum. How can I find out a

So I have a friend putting his Crypto into Nexo.io and I am 100% sure these are scammers as well, promising of up to 20% yields per annum. How can I find out and warn him (with more data)?