Mediaboss Marketing

If you ask most people to name the two most popular social networking sites in the U.S., they'll likely mention Facebook and Twitter . Yet a recent survey by Pew Research Center found that Facebook ranked first in usage among online American adults with a 71% usage rate, but Twitter ranked fifth with just 23%. LinkedIn ranked second, followed by Pinterest and Facebook's Instagram. Why is Twitter falling behind these other networks, and should investors be worried?

Twitter's mobile app. Source: Google Play.

Two things that matter the most to social networks In the social networking industry, two things matter the most -- MAU (monthly active user) growth and ARPU (average revenue per user).

Pew's survey confirms fears that Twitter's MAU growth is slowing down. Back in the fourth quarter of 2013, MAUs rose 30% year-over-year to 241 million. But in the fourth quarter of 2014, MAUs only climbed 20% to 288 million. The good news is that Twitter is generating more revenue per user with new marketing tools, which helped ARPU rise 64% annually to $1.66 in the fourth quarter.

Pew's survey bodes well for LinkedIn, but the professional network isn't faring that much better than Twitter. LinkedIn's registered members rose 25% year-over-year to 347 million in the fourth quarter, but that's a notable slowdown from the prior year quarter, when its user base grew 37%. Based on its registered users during the quarter, LinkedIn's ARPU rose 15% annually to $1.85. Instead of reporting MAUs, LinkedIn reports "unique visiting members," which grew 23% to 93 million per month last quarter.

LinkedIn's mobile app. Source: Google Play.

Instagram reported that its MAUs doubled from 150 million to 300 million between Sep. 2013 and Dec. 2014, but its revenue has never been officially reported. However, analysts at Cowen & Co. expect Instagram to generate $700 million in revenue in 2015 and $5.8 billion by 2020. eMarketer believes that Instagram's U.S. user base will grow about 20% annually in 2015. If overseas MAUs rise at the same rate, MAUs could hit 360 million by the end of 2015, giving Instagram an estimated quarterly ARPU of around $0.49.

The two things that Twitter lacks Beyond MAU and ARPU growth, Twitter lacks two important qualities -- focus and profitability.

Read more here:
Can You Guess the 2nd Most Popular Social Media Site Among U.S. Adults? (Hint: Its not Twitter)