If you have some of their details like where they come from, email address or names, you can try social websites like Facebook. You can also try online people search engines like WhitePages.com: WhitePages and PeopleFinders. You can get more of these websites at http://www.pcworld.com/article/151556/usesensitive.html.
I think you need to go to something like ancestry.com and put in their name. Then you use history records to find out what state or zip code they have. Then if they are registered you can probably find their phone number, you could ask them to meet you for coffee or something