In all likelihood, the member has changed their nickname to one that you don't recognize. If they were on your Hot List, you should be able to find them here. If they were not on your Hot List, you can use the Search facility to look for matching details and relocate them; once you have, you should use the 'Add to Hot List' button at the bottom of their profile.
If the above doesn't work, the member is probably no longer active. Members can deactivate/reactivate their profile as they see fit.
If you can't find someone who you previously had seen then you must assume that they no longer wish to be contacted via users of this site.
Whilst their profile page is offline, we are not able to give out any contact information, and neither can we contact them on your behalf.