You are probably using the wrong Search area.

When you're in an "area" what you type in the search "box" to the right, will only be looked for in this area. For example. if you're in the "i've found it" area, the search box will only look for what you typed in the "i've found it" area.

If however, you use the seach "tab", (top left, and under the "signing in" pane), this will search the whole site (lost & found). This is the one that you should normally use.

The Search button to the top right of the header is for searching the web: not the site. (We left it on becasuse we thought it may be useful).