How to make search functionality faster in asp.net web application.

I always wonder when I look serach functionality of Google,Facebook and Twitter. Can I apply this type of superfast seraching functionaltyIn my asp.net web application. In my application I want to serach a word from huge records in sql server 2008. I dont want to disaplay all records. But when I type some words in textbox by using Auto complete Extender of ajax the records should come faster. If I type the full username for example microsoft than my search functionality should find this word in millions of records in database.
Which is the best method can use to make my search fuctionality very much faster? I dont want to serch word in full paragraph. I want to search word like small username from database from username column which has millions of records (usernames).
Best example - In twitter's search box we search @username or #topic.  


 
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