200 million Tweets flow through the Twittersphere daily

Micro-blogging service Twitter said its users now send short messages called tweets more than 200 million times every day.

Whether the messages convey bits of conversations, the latest news or something from one of the site’s thousands of novelty accounts, the steady stream of tweets has turned into a firehose of updates. The site has more than 300 million registered users who fire off quick messages in 140 characters or less. The company was valued at $3.7 billion after its most recent round of funding in December, though it is probably higher now.

Twitter users sent two million tweets a day in January 2009 and 65 million tweets a day on average in 2010, the company said. While the site is incredibly popular, it has had some trouble finding effective ways to monetize the service. The company introduced “promoted tweets” last year to help monetize the service and it also runs promoted trending topics.

Twitter recently purchased TweetDeck, a mobile and desktop application that lets Twitter users access multiple accounts and post messages on them simultaneously. Twitter also bought iPhone client Tweetie, transforming the application into its main mobile Twitter app. The company works directly with photo-hosting service TwitPic. Twitter is also encouraging external developers to focus on something other than straightforward Twitter clients.

Here are the most-tweeted topics for the first half of 2011:

News and World Events

1. AH1N1 – Swine Flu
2. Mubarak – former Egyptian president
3. Easter – Christian celebration
4. Cairo – capital of Egypt
5. #prayforjapan – sentiment following the March earthquake and tsunami
6. Chernobyl – site of nuclear disaster in 1986
7. Libia/Libya – country facing a civil war
8. Fukushima – Japanese nuclear power plant
9. William & Kate – newly-wedded Duke and Dutchess of Cambridge
10. Gadafi – Libyan political leader

Pop culture

1. Rebecca Black – pop singer
2. Femme Fatale – newly-released Britney Spears album
3. Charlie Sheen – actor
4. #tigerblood – hashtag popularized by Charlie Sheen
5. Nate Dogg – rapper
6. Anderson Silva – Brazilian mixed martial artist
7. Tom & Jerry – famous cartoon
8. Mumford & Sons – British rock band
9. Bieber alert – referring to artist Justin Bieber
10. Queen Gaga – referring to artist Lady Gaga