Pinterest has the leading mobile app for sharing content, according to a study of iPhone users in the U.S. Mobile insights service Onavo measured the growth in market share for content sharing platforms including Pinterest, StumbleUpon!, Alien Blue, iReddit, 9GAG, and Digg in the second half of 2012.

The analysts found that Pinterest was number one in its category. The image-based network known for beautiful photographs of consumer goods came to the Android, iPad, and iPhone in August 2012. The app grew 33 percent from 7.5 percent of the market share in July to 10.1 percent at the end of December.

“Not only does the 33 percent jump reflect Pinterest’s growing popularity,” wrote the Onavo team, “but it also shows that content sharing platforms have become mainstream with adoption rates on par with Gmail (9.8 percent market share, U.S.) and Groupon (9.75 percent market share, U.S.) and IMDb (9.75 percent market share, U.S.).”

The remaining sites held smaller market shares.

Reddit came in second, but it’s important to note that the popular destination for sharing links, images, and videos has more than one mobile option. iReddit, Conde Nast’s official iPhone app for the platform, shares the market with an unofficial application, Alien Blue, for a combined 3.54 percent of the overall market.

Alien Blue was the more popular of the two, growing from 1.8 percent of U.S. iPhone users in July to 2.4 percent  in December.

That said, iReddit also showed growth at the end of last year, nearly doubling  its market share to 1.14 percent of U.S. iPhone users in December.

Link sharing site StumbleUpon appeared to struggle in the third quarter of 2012, rising to 1.21 percent of U.S. iPhone users in November and dipping slightly in December.

reddit competitor 9GAG, a site for sharing memes, showed a significant amount of growth at 136 percent in the second half of 2012. However, with 0.66 percent of the market share, 9GAG’s app still hasn’t caught up to either of reddit’s.

Despite an overall decline in popularity, Digg came out with a new app at the end of July, prompting a 128 percent jump in market share from 0.2 percent in July to 0.4 percent in December. “Still, if we were doing this report in 2009 it’s likely that Digg would have a far higher market share,” the Onavo team wrote.

Not included in the study were blogging platforms like Twitter and Tumblr, on which people also share links and other media; and Instagram, a Facebook-owned application for sharing personal photos.