Much of it still comes down to skilled journalists doing what they have always done, she said: journalists writing excellent copy and editors writing the winning headlines.
But there are some ways to get ahead on social media.
"Just like in real life, you can't force anyone to love you," she said at the Digital Journalism Days conference in Warsaw today. "Turning viral is about love – but you can give love a little help in the right direction."
Boisen shared some of her key tips for growing and maintaining a strong audience on social media.
Speak to the heart
One of the best performing articles Boisen ever wrote began with her young daughter who, at aged 8, asked her mother for a bra.
The resulting story spoke to women all over Sweden in its concern over children's development, peer pressure and motherhood, making the story one of the most shared and discussed on Facebook.
The story was a prime example of "speaking to the heart", she said, of thinking about personal values and company values and how they fit with the readership.
People on social media, and Facebook in particular, share and discuss articles that matter to them so understanding those values is central to social success.
As well as starting a main Facebook page, Expressen has smaller, more focused pages around specific issues.
One focuses on society, so every time an article is written "on equality and children" it is published to that page and is shared widely.
Another page is devoted to gun crime in Gothenburg, a serious issue, she said, so any story on shootings in the city is shared on that page and "goes viral every time".
But publishers needn't always start their own pages. Expressen has made a recent habit of buying popular Facebook pages to take advantage of the existing audience and continue speaking to them directly.
One such example is a Swedish page with 300,000 likes which translates as 'We who love to cuddle up on Fridays', a positive page which shares stories on "how to make the perfect taco, or how to have a wonderful love life".
These are regular magazine supplement stories for news outlets all over the world, and in buying the page Expressen bought the audience to speak to them directly with their own stories.
Make a difference
"Anger is a fantastic viral feeling", said Boisen, and news organisations can marshal that emotion for positive societal change.
With the #VoteGBG campaign, Expressen led public anger at politicians' broken promises over a congestion tax on vehicles, forcing a referendum.
Although anger can be a motivator on social media, so can laughter, and Expressen tried setting up other pages for humour on Facebook and Twitter.
They were not always a success, said Boisen, but if they were to fail they should "fail fast and fail cheap".
"Done is better than perfect," she said, and like in any walk of life it is better to try, fail and learn than never try at all.
She also shared 10 main tips for success on social media:
1. Practise, practise, practise.
2. Be first to talk about an issue.
3. If you're not first, be the best.
4. Like, share and be generous.
5. Don't be shy to follow lots of people.
6. Go fishing for hashtags and conversations.
7. Be polite and be a good example.
8. Choose the right platform for the conversation.
9. Be active, reply to people.
10. Be positive, share good news.
Update: This article originally has been updated to show that Expressen, not its Gothenberg edition GT, has more than 1.5 million followers across its Facebook pages.
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