Twitter recently posted an update regarding those missing from the Find People Search on Twitter.
We’ve updated this Known Issues page to include the issue of “searching for usernames with underscores.” Search is aware of this and we’ll update this page when it’s resolved.
To find Twitter accounts and follow them, access here
If you have or know someone that has a Twitter username with sn underscore in the name, stay tuned for updates here
Watching out for you, one tweet at a time -Twitter Watchdog