Is there a twitter follow app?

[Amal]

You can do it manually.
1.Go to Twitter Search.
2.Search for a hashtag you want to track. Include the “#” in your search query. Here’s a search for #facebook
3.Keep that page open in a browser tab, and refresh it periodically to see the latest results. Or subscribe to the feed for your search in your feed reader, and check there occasionally for updates.
Or you can use tweetdeck.com/ for the same. Hope this helps. Choose as best answer if it helps you.