Who in Twitter's top 5 do you follow?

Lady Gaga became the first Twitter user to reach 20 million followers on Tuesday, beating runner-up Justin Bieber to the social media milestone.

The Poker Face singer was an early adopter of the social networking website when she joined Twitter in March 2008. She has held the top Twitter spot since taking the title from Britney Spears in 2010.

Unlike some celebrities whose managers do the tweeting, Gaga has claimed to maintain her Twitter presence personally, using it to interact with fans, post announcements about tours and releases, and share pictures.

Data from Twitter Counter, a website that tracks Twitter statistics, show Gaga's follower growth rate is consistently higher than that of Bieber, who is about two million followers behind.

In addition to her Twitter following, Gaga has nearly 49 million fans on Facebook.

The top five people most followed on Twitter all come from pop music.

1. Lady Gaga - 20,193,595

Listening to HAIR, singing into hairbrush. I think I forgot I'm a pop singer for 5 whole minutes + then remembered I GET TO TOUR THIS SHIZ!

-- Lady Gaga (@ladygaga) February 22, 2012

2. Justin Bieber - 18,143,515

i dont plan on ever losing any fans. young or old. only gaining more and more respect. MJ never left the kids he just grew with them.

-- Justin Bieber (@justinbieber) March 5, 2012

3. Katy Perry - 15,786,523

I think in a past life I might have been an a top notch juggler... cause multitasking is my favorite thing to #efficacyisfun #weirdtweet

-- Katy Perry (@katyperry) February 26, 2012

4. Shakira - 14,591,933

I just saved a ladybug's life...It think it will be a good day! Shak twitter.com/shakira/status...

-- Shakira (@shakira) March 6, 2012

5. Rihanna - 14,539,163

Literally craawwwled to the plane! NO SLEEP!!! #AreWeThereYet

-- Rihanna (@rihanna) March 1, 2012

(This survey is not scientific. Results are based on readers' responses.)