With Facebook and Twitter holding steady at 98%, this makes Instagram the fastest growing social network among marketers worldwide, with nearly 200 million users.

That is according to social media analytics company Simply Measured, which has released its latest Instagram brand adoption study. The key findings are:

• 71% of the Interbrand 100 use Instagram. This is up from 40% in October 2012. While Facebook and Twitter hold steady with 98% coverage, Instagram is the fastest growing social network among marketers worldwide.
• As activity increases, so do followers. 57% of top brand marketers are now averaging at least one post per week, up from only 38% in Q3 of 2012. As a result, more than one third of top brands have 10,000 followers and 19% enjoy audiences that exceed 100,000 followers.
• Engagement is skyrocketing. Brand engagement has grown by 350% year over year, due in part to a 70% increase in brands posting to the visual network.
• Automotive, media and luxury brands dominate. Mercedes-Benz, BMW and Audi make up three of the top five most engaging brands. In total, the top ten brands received 83% of all Instagram engagement, while accounting for 33% of all posts.
• Photos receive more comments and likes than videos. Like most new features, video adoption has been slow to gain momentum, accounting for only 6% of total posts. Meanwhile photos continue to lead the way, driving 26% more engagement than videos.
• Hashtags have become the norm. 83% of Instagram posts include at least one hashtag, with 63 of the 65 active brands on Instagram using the new feature. Of interest, top brands use hashtags more sparingly than other brands.

The full report can be found here.