All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
You are permitted, Allaah willing, to travel for Hajj without informing anyone of those to whom you suggested to invest their money with your friend. Advising them to invest their money with your friend is not a sound reason for them to ask you to compensate them for the loss they incurred. Indeed, you may appoint some scholars and righteous people to arbitrate between you so that they would convince them that they have no right to ask you for any compensation. For more benefit, please refer to Fatwa 85639.
As regards your friend, if he really did so, and you are able to contact him, then it is an obligation to advise him and order him to give back people's rights, and remind him of the bad outcome of injustice. Indeed, it is confirmed that the Prophet said: "Beware of injustice, as injustice is darkness on the Day of Judgement." [Muslim]
Furthermore, the Prophet said: "Whoever takes people's money while wanting to repay, Allaah would help him to repay, and whoever takes people's money while wanting to spoil them, then Allaah will spoil him (i.e. spoil his wealth and punish him in the Hereafter)." [Al-Bukhari]
Finally, it should be noted that if this man is a co-partner and he is the one who used to run the business, then he incurred a loss, in this case he is only responsible if he was negligent. For more benefit, please refer to Fatwa 85867.
Allaah Knows best.