MINNEAPOLIS: Instagram, the photo-sharing network, has become the most popular social media site for US teenagers, according to the autumn findings of a bi-annual study of teenage attitudes across 41 states.

Based on the responses of 7,200 US teens with an average age of 16, the latest "Taking Stock With Teens" results from Piper Jaffray, the investment bank, found about three-quarters (76%) now use Instagram, up from 69% in its previous report.

Facebook, once the most popular site, has witnessed a significant fall in popularity from 72% to 45% and has been overtaken by Twitter, Marketing Charts reported.

Twitter is now the second most popular social media site, used by 59% of US teenagers, although this too is a decline on its 63% usage recorded six months ago.

Pinterest and Tumblr are used by 22% and 21% respectively while 14% use "other" social media sites, including Snapchat (4%).

Of particular note for marketers, the report found 38% of US teenagers believe Instagram is a favourable marketing channel to reach them, a view shared by 34% about Twitter and 21% about Facebook.

"Teens use social media, mainly Instagram, to create their own unique personal brands and seek peer affirmation," explained Steph Wissink, co-director of research at Piper Jaffray.

Amazon is by far their preferred shopping website (32%), followed by Nike (8%), eBay (5%) and Forever 21 (5%) while 2% each opt for Urban Outfitters, Victoria's Secret, American Eagle, Nordstrom, Pacsun, Brandy Melville and Eastbay.

Apple remains the top consumer electronics brand for teens. In all, 67% own an iPhone, up 6% from spring 2014, and almost three-quarters (73%) expect their next phone to be an iPhone.

Over half (54%) own an iPad, 12% have an iPad Mini, while 16% own an Android tablet, 6% own a Kindle Fire, and 7% have a smartwatch.

In other findings, food is their second largest spending category (20%), behind clothing (21%) and ahead of accessories/personal care (10%).

The average spend on fashion goods per year has risen to $1,069, up from $995 annual spend recorded in the same period last year, and Nike is the top preferred clothing brand for almost a quarter (22%), followed by American Eagle (8%) and Forever 21 (7%).

Data sourced from Piper Jaffray, Marketing Charts; additional content by Warc staff