"I created the account the day before I was admitted to hospital," Eriksson tells Radio Sweden. "I had seen on Instagram that a lot of people supported each other and I felt like I needed to be part of that support system. It's like a family... It's people who have been through the same things, so you become very close. Other people can say they understand, but if you've never been through mental illness or eating disorders, you can't really relate," says Eriksson.
In many ways, Eriksson is just a regular teenager. She is still in school and in her spare time she likes to work out, cook and spend time with friends and family. But she also has a huge following online, with over 30,000 people subscribing to her posts on Instagram and reading her blog.
Just 15 months ago Antonia ended up in hospital after nearly starving herself to death. She had become obsessed with counting calories, she says, spending more and more time in the gym, while eating less and less. By the time she was admitted to hospital, she weighed just 38 kilos. It was from the hospital bed that she posted her very first Instagram picture.
"The first account was about my fight against anorexia, about recovery. When I changed my name it was because I felt like I had changed as a person. The focus was no longer on recovery, it was being recovered."
Antonia changed her Instagram handle from @fightinganorexia to @eatmoveimprove. Now she focuses on good food, healthy lifestyles and staying fit. She posts "selfies" from the gym and pictures of her meals and workout outfits. In Instagram terms, she has moved away from "thinspo" and has come closer to "fitspo".
"Thinspo is a pro-anorexia hashtag," explains Eriksson. "It's mostly people who are ill themselves who create thinspo accounts. They encourage you to stay sick...Before I got help and was admitted to hospital, those accounts are what helped me starve myself. They're meant to make girls feel awful about themselves and they succeed."
There is a thin line between "thinspo" and "fitspo" accounts, says Eriksson, but the latter are meant to be positive, emphasising fitness and health.
"They're both objectifying women," Eriksson warns. "I choose not to put my account in either categories. I'm careful about what I post. It's about inspiring people to be healthy...I never post numbers as that doesn't define health. If people ask me how much I weigh, how many calories I consume or how I lost weight, I don't answer. The way I lost weight almost cost me my life."
Social media can be both destructive and positive for young girls, says Eriksson. Many go online for "thinspiration" - ideas for how to get skinny - using hashtags like "thinspo" and "proana". But young people are also using social media to support each other and to spread positive body images.
Eriksson says social media platforms have a big responsibility in all this. Instagram previously blocked negative hashtags, but now they are searchable again.
Social media have also changed the terms for organisations fighting eating disorders. Hanna Kihlander is a spokeswoman for Frisk och Fri, meaning "healthy and free". Her organisation has had to rethink how they reach and talk to young people, moving away from the traditional telephone hotlines and leaflets to setting up online chats and Facebook communities.
"We are trying to reach young people with something different and we try to write about things we see young people talking about on other platforms. Social media are both a challenge and an opportunity for us," Kihlander tells Radio Sweden.
Eriksson thinks social media platforms offer great opportunities for awareness-raising campaigns.
"Since so many youths are on social media today, it's the perfect platform and support groups should use it because they could reach and help so many people," says Eriksson, adding: "We need more people who tell their stories. That's the main reason I'm happy my story has spread. People need to see that it's possible to recover because when you're sick, it feels impossible."