Example of a search form, searches with Google in portfolio.*.utwente.nl
(Portfolio sites of students of Industrial Design and Create).
How it works:
<form id="search" method="get" action="https://www.google.com/search">
<input type="text" size=20 name="q">
<input type="hidden" name="sitesearch" value="portfolio.*.utwente.nl">
</form>
portfolio.cr.utwente.nl/student/xxxxx
Alternative: Google Custom Search Engine.
To search inside a page, you can use a jQuery Plugin like Tipue or Searchable.