Limit user search?

Is there a way to limit the users shown when searching to grant them access?

As well as the standard 'authenticated user' im using an additional role of 'editor'. Editors will be able to grant access on node's they've created. Editors will also be able to create users.

I need to limit the user's that can be given access to content (by the editor) to users that were created by that editor.

Thanks