Video app Socialcam once again topped our list of the fastest growing Facebook applications by monthly active users this week.

Titles on our list gained the most MAU of any apps on the platform, growing from between 900,000 and 15.7 million MAU, based on our AppData tracking service.

Top Gainers This Week

Name MAU Gain Gain,% 1.  Socialcam 69,900,000 +15,700,000   + 29% 2.  21 questions 18,300,000 +7,900,000 + 76% 3.  Zynga Bingo 7,800,000 +5,700,000 + 271% 4.  Truth Game 5,800,000 +2,400,000 + 71% 5.  Bubble Safari 4,000,000 +2,200,000 + 122% 6.  Scribd 23,900,000 +1,900,000 + 9% 7.  Candy Crush Saga 10,500,000 +1,600,000 + 18% 8.  MyCalendar – Birthdays 32,800,000 +1,600,000 + 5% 9.  Between You and Me 8,900,000 +1,400,000 + 19% 10.  Lost Bubble 3,300,000 +1,300,000 + 65% 11.  My Friend Secrets 3,800,000 +1,300,000 + 52% 12.  Bubble Blitz 3,100,000 +1,200,000 + 63% 13.  Truths About You 5,400,000 +1,200,000 + 29% 14.  Birthday Calendar 2012 ★ 3,300,000 +1,100,000 + 50% 15.  Pyramid Solitaire Saga 4,300,000 +1,100,000 + 34% 16.  DoAlbums 1,500,000 +1,080,000 + 257% 17.  Photo Contest 5,600,000 +1,000,000 + 22% 18.  Get Revealed 3,200,000 +900,000 + 39% 19.  Instagram 18,000,000 +900,000 + 5% 20.  Skype 16,000,000 +900,000 + 6%

Socialcam continues to burn up the charts as it approaches 70 million MAU. Most of that number seems to come from new users adding the app, as we can tell from Socialcam’s high number of daily active users but relatively low DAU over MAU percentage. Unless Socialcam can find ways to regularly engage its existing users, we’re likely to soon see a sharp decline in MAU. Facebook has also recently implemented some changes that could reduce the frequency of Socialcam stories in users’ feeds.

Canvas-based quiz app 21 Questions took the No. 2 spot this week after seeing an overall decline in MAU since March. Other quiz apps – Truth Game, Between You and Me, My Friend Secrets, Truths About You and Get Revealed – followed nearly the exact same growth trends, indicating that over the past two weeks Facebook has made some change leading quiz apps to gain traction again.

Instagram saw a bump in MAU this week after a mostly slow May. The increase could be the result of a new feature we discovered last week that puts an Instagram icon in users’ mobile feeds to direct users to the native Instagram app.

Zynga Bingo led games on the platform, though five others made the top 20 this week.

All data in this post comes from our traffic tracking service, AppData. Stay tuned for our look at the top weekly gainers by daily active users on Wednesday, and the top emerging apps on Friday.