The search function contains the so-called 'stopwords'. They're regular words that if used within a search, would eat up the system's resources. These are common words like Undernet, username, etc.
If all you're getting is a blank page, it's because you're probably attempting to search for a common word that wasn't defined as a stopword yet.
The Search function permits operands aswell, for example
Channel AND Service
When else fails, you can always try google, as this website is indexed by search engines.
Just search for "your-keywords site:forum.undernet.org"
Hope this helps,