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:

- 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.

- 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.

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

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

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

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

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

- 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.

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

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

- 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.

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

- 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."

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

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