The International Committee of the Red Cross have uploaded records of soldiers and civilians captured during the First World War to the web.
Archives 1914-1918: during the First World War, 10 million people, servicemen or civilians, were captured and sent to detention camps.
The belligerent countries involved provided lists of prisoners to the ICRC, wich created an index card for each prisoner and detainee. Now, you can search through all 5 million of them.http://grandeguerre.icrc.org/ This is still a work in progress so if you expect to find someone and cannot, check back in a few weeks.