firstly, it's dissuade. not persuade.

secondly, it's a known fact that most pyramid scheme after 4th layer is unsustainable. if he's still in the 2nd or 3rd layer, i would not advice against it but be extremely cautious and take the money off the table when risk fluctuates.

if he's in the 4th layer or more, tell him it's pouring good money into salty sea.