Twitter growth slowdown?

Recap: I'm in the middle of a month-long experiment tracking the Top 500+ Twitter users (based on Followers). I decided to look at the growth rate of the accounts to see what, if anything, it indicated about Twitter culture.

Last week, it became apparent that the Twitter list of Suggested Users (found under the "Find People" tab on Twitter) almost completely accounted for the rapid growth of the fastest growing Twitter accounts. Here is the most recent list:

Fastest growing Twitter accounts (5/4/09-5/10/09):

1. Justin Timberlake (@JTimberlake) 361%
   
2. Good Health (@GoodHealth) 355% SU
   
3. Life (@Life) 254% SU
4. Counting Crows (@CountingCrows) 210% SU
   
5. ExecTweets (@ExecTweets) 172% SU
   
6. Wyclef Jean (@Wyclef) 164% SU
   
7. White House (@WhiteHouse) 118% SU
   
8. Joel Stein (@TheJoelStein) 115% SU
   
9. iTunes Movie Trailers(@iTunesTrailers) 105% SU
   
10. Roc4Life (@Roc4Life) 92% SU
    
11. Kevin Nealon (@Kevin_Nealon) 84% SU
    
12. Jack Welch (@Jack_Welch) 83% SU
    
13. Nick Swisher (@NickSwisher) 79% SU
    
14. UNHCR Refugee News (@Refugees) 75% SU
    
15. Serena Williams (@SerenaJWilliams) 71% SU
    
16. John Green (@RealJohnGreen) 62% SU
    
17. Fantastic (@ShowDavida) 60% SU
    
18. Soraya Darabi (@Sorayad) 59% SU
    
19. Mano Menezes (@ManoMenezes) 55% SU
    
20. Etsy (@Etsy) 55% SU

SU=Twitter's Sugested User

Almost all of these accounts were added to the Twitter Suggested Users list in the past 2 weeks. Since the Suggested User list is such an overwhelming influence in determing which accounts grew the fastest, I eliminated the 208 names of Twitterers selected by Twitter staff and got this alternate list of the fastest growing accounts not affected by a SU recommendation:

Fastest organically growing Twitter accounts (5/4/09-5/10/09):

1. Justin Timberlake (@JTimberlake) 361%
   
2. Pink (@Pink) 50%
3. Ben Stiller (@Ben_Stiller) 48%
4. Joy Behar (@JoyVBehar) 42%
5. Paris Hilton (@BabyGirlParis) 39% 
6. Emily Osment (@EmilyOsment) 36%
7. Lauren Conrad (@LaurenConrad) 31%
8. Drizzy Drake (@DrakkarNoir) 28%
9. Alyssa Milano (@Alyssa_Milano) 28%
10. Matthew Perry (@LangfordPerry) 27%
11. Trey Songz (@SongzYuuup) 26%
12. Lauren London (@MsLaurenLondon) 23%
13. Russell Simmons (@UncleRush) 22%
14. Sarah Silverman (@SarahKSilverman) 22%
15. Terrence J (@TerrenceJ106) 21%
16. Hugh Jackman (@RealHughJackman) 21%
17. Khloe Kardashian (@KhloeKardashian) 21 %
18. Nathan Fillion (@NathanFillion) 20%
19. Lil Wayne (@WeezyOfficial) 19% (account has recently been hacked)
20. Keri Hilson (@MissKeriBaby) 18%

There are a lot of the same user accounts as in last week's alternate Top 20 list, mostly pop culture TV/Movie/Music/Reality show celebrities. But in general, in the Top 500+ accounts, growth in Follower numbers is slowing down considerably. 

As far as I've been able to determine, from its creation in March 2006 to September 2008 Twitter growth was marked by a slow but steady increase in both the number of Twitter accounts and the number of Followers in the majority of accounts that are not protected (that is, Followers admitted by approval only). 

During Summer 2008, Twitter started growing faster and this growth took off during the latter part of the Presidential Election (October 2008). This increase accelerated even faster between December 2008-midApril 2009 as Twitter received both media attention--news shows, newspaper/website articles, Twitter founders' appearances on Oprah, The View & The Colbert Report--as well as an influx of aggressive Internet Marketers and ECommerce business people eager to put Twitter to work for them through Auto-Following strategies.

But, if the largest accounts are a reflection of trends on Twitter in general, this exponential growth rate in account size is slowing done considerably. 

Last week, 74% of the Top 500+ accounts had a growth rate of 10% or lower compared to 56% (5/3/09), 50% (4/26/09) and 34% (4/19/09). 

Median rate of growth for the Top 500+ accounts fell from 13.35% (4/19/09) > 10.67% (4/26/09) > 9.29% (5/3/09) > 7.01% (5/10/09). 

This slowing down or "plateauing" is most evident in accounts that have existed for six months or longer.

I can see a few possible reasons to account for the slowdown in growth of account size:

1. The saturation of media coverage has led to a decrease in creation of new Twitter accounts
2. Twitterers are cutting down on the number of people they follow (downsizing)
3. People are choosing to go broader in their selection of people to follow (few celebrities & "top" names, more fellow users)
4. Twitters who aggressively try to build high Follower numbers are slowing down their efforts (due to influx of celebrities & new Following number limits imposed by Twitter)

These are just hypotheses based on a highly selective group of Twitters I've studied over a very short period of time. But it could signal that growth in Twitter is slowing down or has reached a plateau. 

No doubt it is likely Twitter will experience bursts of rapid growth in the future as it becomes more mainstream, more well-known people publicly talk about their Twitter use or Twitter increasingly becomes a source for breaking news. We'll see if this slowing down trend continues over the next two weeks of this project or whether it is just an anomaly.