Teenage Instagram star Essena O'Neill who amassed hundreds of thousands of followers online has turned her back on social media, branding it "unhealthy".

The 19-year-old announced a week ago that she is quitting Instagram, YouTube and Tumblr, where she has posted thousands of photos and videos.

"Without realising, I've spent majority of my teenage life being addicted to social media, social approval, social status and my physical appearance," she wrote.

"Social media, especially how I used it, isn't real. It's contrived images and edited clips ranked against each other. It's a system based on social approval, likes, validation in views, success in followers. It's perfectly orchestrated self absorbed judgement."

In a 17-minute YouTube video posted online yesterday, O'Neill said that despite being surrounded by "all this wealth, all this fame, all this power...I had never been more miserable. I'm the girl that had it all. And I want to tell you that 'having it all' on social media means absolutely nothing to your real life.

"Everything I was doing was edited and contrived to get more value and to get more views."

O'Neill has deleted 2,000 photos from her Instagram account that she said "served no real purpose other than self promotion" and edited the captions on many of those she retained to be more honest. She says she would pose for photographs in outfits she wouldn't even leave the house in, and restricted her diet and "excessively" exercised to maintain her tiny figure.