Dear Javed, Assalamu Alaikkum.
Here you are talking about haq. The money you owe to someone is their haq and it should be paid back. It is strange that you have taken money from your friends or colleagues and you do not know their details or contact inforamtion. However, I am sure that you will be aware of their nationality. All of those guys will be remembering you. It would have been more appropriate for you to take their contact details before you leave Moscow. I am not in the level of a person who can give some fatwa on this issue. It will be better to contact someone who knows more about such a serious issue. Ask the same question in the Ask the Scholar column of ISLAM ON LINE. You may find it in
www.islamonline.net. There are plenty of scholars who will look into your question and will give you the right answer.