Searching for a user details (including custom fields) in People Administration Page
I recommend using Views.  With this you can create a searchable, sortable and filterable display using any format you desire, and including any fields you want.


  You need Views if
  
  You like the default front page view, but you find you want to sort it
  differently. You like the default taxonomy/term view, but you find you
  want to sort it differently; for example, alphabetically. You use
  /tracker, but you want to restrict it to posts of a certain type. You
  like the idea of the 'article' module, but it doesn't display articles
  the way you like. You want a way to display a block with the 5 most
  recent posts of some particular type. You want to provide 'unread
  forum posts'. You want a monthly archive similar to the typical
  Movable Type/Wordpress archives that displays a link to the in the
  form of "Month, YYYY (X)" where X is the number of posts that month,
  and displays them in a block. The links lead to a simple list of posts
  for that month. Views can do a lot more than that, but those are some
  of the obvious uses of Views.