15 must know facts about the global phenomenon called Twitter

Twitter, which Thursday revealed its plans to go public, came to life on March 21, 2006 when co-founder Jack Dorsey's account (@jack) automatically sent out the first tweet, which read: "just setting up my twttr."

Dorsey followed it up with the first "human-generated" tweet: "inviting coworkers." More than 170 billion tweets have since gone out worldwide. Twitter said on Thursday that it had 218 million active users, as of June.

Some facts about a global phenomenon:

1. Justin Bieber (@justinbieber) has the most followers with 45,366,914 as of 2200 GMT Thursday, followed by Katy Perry (@katyperry) with 44,122,303 and Lady Gaga (@ladygaga) with 40,229,059.

2. US President Barack Obama (@barackobama) is fourth with 37,501,850 followers; the announcement of his re-election victory in November 2012 was re-tweeted more than 800,000 times.

3. The average Twitter user has 208 followers and spends 170 minutes on the site every month.

4. There are more than 200 million active Twitter users. Eighty percent of all users access Twitter on mobile devices.

5. About 20 million Twitter accounts are believed to be fake.

6. The hashtag (#) feature on Twitter which groups tweets by subject debuted in August 2007, having been proposed by a user.

7. In October 2009, Google and Microsoft began integrating tweets into their search products.

8. In January 2013, Twitter introduced Vine, which enabled users to make and tweet six-second looping videos. Some 12 million Vine videos are uploaded every day.

9. Twitter is based in San Francisco, with additional employees in New York, Chicago, Los Angeles and Washington. Its total payroll exceeds 900.

10. Prior to Thursday's IPO announcement, many analysts valued Twitter at around $10 billion. By comparison, Facebook went public valued at $16 billion.

11. Twitter was incorporated in April 2007, the month after it stole the show at the influential South by Southwest technology and indie music festival in Austin, Texas.

12. It was co-founded by Biz Stone, Evan Williams and Jack Dorsey -- @biz, @ev and @jack.

13. Asked by AFP in March 2011 why Twitter is such a hit, Stone replied: "A big part is that it is just very simple and connects people to other people they would not otherwise be connected to."

14. The initial Twitter logo was created by Stone, a former graphic designer.

15. Twitter chief executive Dick Costolo is a former improvisational comedian.