Like I said before, I really don't know enough about what you're doing to be able to tell you how to write it.
In general when someone asks how to eliminate a large switch statement or a large stack of if/else blocks, the command pattern comes to mind.
This might not be the best solution for you. Only you can make that decision.
From what I've heard so far, and if each text field requires a separate search anyway, it shouldn't be hard to loop through all fields in the form and execute a search on its contents if its not empty.
On the other hand, if some of the fields are subtractive (new WHERE clauses to a SQL query) then this approach might be very inefficient and the if/else blocks to build up a single query might actually be your best approach.
Only you can tell.
If you're familiar with the command pattern, then
you should be able to make this determination.
-Ben