It's a Thursday night in June and a chorus of boos is swamping the Troxy theatre in east London. A group of baby-faced pop-punk revivalists from Australia have scooped best international newcomer at the Kerrang! awards, and the audience are far from pleased for a band who seem to have arrived overnight.

Six days before and 15 miles across the city, however, Michael Clifford, Calum Hood, Luke Robert Hemmings and Ashton Irwin of 5 Seconds of Summer are greeted by a very different cacophony: the best part of the 90,000 people who have come to Wembley Stadium to see One Direction are screaming at 5SOS, who are supporting, with the kind of mania only ever granted to a massive boyband.

5 Seconds of Summer are a phenomenon. An updated Busted with global appeal and better looks, they are the logical next step for 1D fans who have entered their teens and fancy something a little less tepid; who want songs about snogging in libraries and hating their hometowns. Thankfully for 5SOS, those kind of fans exist in abundance: at the time of writing, the group have more than 3.5m followers on Twitter, 1.6m on Instagram, a YouTube account boasting 89m views and 5.2m likes on Facebook. Their debut single topped the iTunes charts in 39 countries on pre-orders alone, while their self-titled debut album was only prevented from entering the UK charts at No 1 by all-conquering internet overlord Ed Sheeran.

As well as selling out headline tours in Australia, the US and the UK (their 2013 Camden Barfly show sold out in 2.3 seconds), they supported One Direction at seven O2 Arena shows before they'd even released their first single. There was even an unexpected 10% surge in sales of men's American Apparel underwear earlier this year, which was attributed to the garment's product placement in the lyrics of their million-selling single She Looks So Perfect. They've got the right media backing, too: the alternative press are keen, with nods from Rock Sound and, as previously mentioned, Kerrang! George Ergatoudis, the head of music at Radio 1 and 1Xtra, became a supporter following reports that the band's early gigs were a hive of hysteria ("There's something serious going on, because the fans are rabid and there's a lot of them," was one BBC staff member's response on seeing them play, he says). So how did they get to this point?

5SOS's story seems straightforward enough: three pop-punk loving teens from the Sydney suburbs meet at school. Hemmings (vocals/guitar) sets up a YouTube account to post Bieber-nuanced cover versions, before being joined by Clifford (vocals/guitar) and Hood (vocals/bass). On 3 December 2011, the trio play their first gig at a local hotel in front of 12 people. After recruiting drummer Irwin via Facebook messages, they begin to take the band more seriously, writing their own material, playing venues across Sydney, uploading more covers and watching their social media fanbase grow.

What happened next, however, was more of a leap. Following an Australian tour with US band Hot Chelle Rae, 5SOS went from being a group of web-savvy teens with a growing following at home to trekking across the globe to live in London. They were then invited on One Direction's 2013 Take Me Home arena tour, and within the space of 10 weeks, the band went from playing a mid-sized venue in Adelaide to the 20,000-capacity O2 Arena in London.

According to Nick Raphael, the president of their label, Capitol, 5SOS's spectacular rise is easily explained: the band's British-born and Australia-based manager Matt Emsell introduced them to management company Modest, the all-powerful firm run by Richard Griffiths which also looks after One Direction (it's no surprise, then, that 1D have been hugely supportive since 5SOS's YouTube days and have songwriting credits on the band's album).

That's more or less all that we're allowed to know for now. It becomes clear that those who work for Modest are kept more under lock and key than the prisoners of Alcatraz. Griffiths, despite being the first international agent for AC/DC and a former president of BMG, doesn't even have a Wikipedia page. Despite weeks of requests, the team from Modest will not speak to the Guardian about the band's formation, finances and future.

On Tuesday 1 July, a group of 5SOS fans are waiting outside a townhouse 20 yards from the BBC's Broadcasting House, in pursuit of the band. It's been an early start for 5SOS, who have just visited Nick Grimshaw's Radio 1 Breakfast Show and are now facing a day's press. Polite and relatively unstarry, they squeeze on to a sofa. Hemmings is mysterious – either quite shy or very sullen; Irwin is so good-looking and confident that it's as if he's a Syco test-tube creation; Clifford, with his green hair and skate-punk image, acts the wide-eyed bundle of charisma; the sweet and handsome Hood shows off his biceps in a ripped Unknown Pleasures vest (vintage band T-shirts are integral to 5SOS's image: "You can tell our fans from a mile away, they're the ones wearing Nirvana shirts," Irwin says).

Some of the animosity from the rock world may spring from their attractive, squeaky clean-cut image, which no number of vintage T-shirts can dispel. They counter by asserting that they are not, in fact, good-looking. "I hate that when I see it online – 'Why would I like 5SOS when you can like someone else who is much more good-looking?' It's not just about that. Were the Rolling Stones good looking?" asks Irwin. "Well Jagger was, but the rest of the dudes? Maybe not so much."

Aesthetically and sonically inspired by the pop punk of the early 00s – from the juvenile, Jackass rebellion of Blink 182, to Good Charlotte's slick sounding anti-everything anthems, and Busted and McFly's cartoon goofiness – 5SOS's intention is to entertain, not inform. "We're never going to write an American Idiot song," Hemmings says (in fact, 5SOS have a long list of writing partners, though all bar one of the songs on their album contains input from the band members). "We're not going to write about politics. Maybe when we're older. But we write about being a social outcast as well as girls and stuff. [She Looks So Perfect is] about running away a little bit. It wasn't our favourite place, where we grew up …"

Being in a band in Riverstone, their suburb, was not easy, they say. Irwin claims to have been "nearly stabbed" multiple times. "It's proper violent," he says. "Which made us stick together, and that's what grew our bond together, because when we met, we realised we're the same. We don't necessarily belong." And nothing is more likely to generate ferocious loyalty among a teen fanbase than the knowledge that their heroes didn't belong either. 5SOS reciprocate by interacting with their fans on social media – band and supporters together, united.

When the quartet signed to Capitol, both the label and the band scored a result: the label got a ready-made rock band with a loyal fanbase, and the band in turn got to work on an album with their pop-punk heroes (among the producers on their album are the Madden brothers from Good Charlotte, Jake Sinclair, who has worked with Fall Out Boy and Pink, John Feldmann, who numbers All Time Low among his credits, and McFly and Busted producer Steve Robson).

The female fans outside Radio 1 – who are furious when the word boyband is brought up ("Not. A. Boy. Band," one says, with terrifying solemnity) – say that through 5SOS they not only met great friends, but picked up instruments and formed bands, too.

With the combination of their awkward teenage charisma, the experience of One Direction's team, Radio 1's belief that rock is due for a return and the waning popularity of X Factor-generated boybands, 5SOS could be the blueprint for the next generation of music industry success stories. For labels fatigued by the reality TV format, YouTube is the new pool for easily groomed talent, and 5SOS are the future: a social-media savvy group who hint at rebellion but create their own viral campaigns.

Perhaps it's not the most enchanting story, or possibly even the most credible, but as Kerrang! editor James McMahon says: "I'm sure that when they're riding around on the back of a unicorn, they're not going to be thinking: 'I wish we'd taken the punk route to success.'"