I would have personally not introduced Bitcoin or Cryptocurrency in general to them, to be honest. It would have been better for him to start talking about it after giving some basic lesson of the most common kind of scams and fraudulent schemes one could find in this market, the reason in obvious.
Perhaps for people like you or I, who have already spend sometime wound here, it is pretty obvious what are the main characteristics of a scam, but for people who are in a desperate state and are uneducated about Bitcoin, it is easier for a scammer in social media or on internet in general to deceive them in order to take the little they have.
Do not misunderstand me though, Bitcoin and cryptocurrencies themselves can be a pretty good option to manage money and invest, but it can be a tool used by criminals to strip away the small savings of the least fortunate members of our society. It is just my opinion though, hopefully those friends of OP are more savvy than the average person and would never fall for a classic ponzi.