Things happen for a reason.
You can't stop your friend from joining.
Unless you know the reason why he/she joins, and come up with
better reasons and alternatives for your very friend to sidetrack
and invest his/her savings into another Better Investments offered
elsewhere. Probably in the banks etc.
Meet your friend for a casual talk, and ask ur friend some
in-direct questions.
If you're completely new to asking such questions.
I can help out, but only during the weekends since I'm busy with
other commitments.
Ask for at least 8%-20% ROI. (This is something which I've read
from a book about creating wealth, haven finish the book yet, so
dun ask me abt the details. I'm still learning.)