Lady Gaga has reached the milestone of 18m followers on the social networking site Twitter.

The 'Born This Way' singer is the most popular figure on the site, 2m followers ahead of her closest rival, Justin Bieber.

Gaga tweeted a thank you to her fans saying, "Can't believe I have 18,000,000 TwitterMonsters, really rad, was just a few years ago I had barely any."

Behind Gaga and Bieber is Katy Perry who has 13.9m followers.

U.S. President, Barack Obama and reality TV star, Kim Kardashian are the only two non music artists in the top ten.

The current top ten of most followed stars on Twitter are:

1. Lady GaGa - 18m followers
2. Justin Bieber - 16.4m followers
3. Katy Perry - 13.9m followers
4. Shakira - 12.6m followers
5. Kim Kardashian - 12.5m followers
6. Britney Spears - 12.4m followers
7. Rihanna - 11.9m followers
8. Barack Obama - 11.9m followers
9. Taylor Swift - 10.4m followers
10. Selena Gomez - 9.6m followers