Is this the coolest teenager in the world?

Tavi Gevinson has been described as "an inspiration" and "a poster child for her generation". But perhaps more dubiously, she is also a 13-year-old girl who has made her name taking photos of herself in her bedroom and posting them on the internet. In March 2008, Tavi, then just 11 years old, started an online diary inspired by her passion for fashion, under the alias "Style Rookie". Ever since, this tiny kid from the suburbs of Chicago has spent the majority of her spare time dressing up in a series of bizarre get-ups, and uploading photos of her efforts for the world to see. It's a hobby that has already brought her celebrity on a scale she can hardly have dreamt of – and today she has millions of followers around the world.

Those keeping tabs on Tavi's progress over the past two years will have noticed that this is a girl who likes to talk, about pretty much anything. Her school play rehearsals: "Tech week ... blah. That means not getting homework done and coming home late every night with 10 pounds of lipstick on, sweaty head to toe from those stage lights, blinding mascara lumps, and so much hairspray you don't even feel your head touching the pillow." Or her latest purchases: "In other news I bought a harmonica necklace ... now I'm one of those assholes that walks around playing it in between sentences and words."

What Tavi likes to do more than anything else, though, is to add to her ever-expanding catalogue of self-portraits, taken with a simple point-and-shoot camera. The first was accompanied by the following note: "Today I wore a skinny headband across my forehead. I also wore a black and white mini-dress with jagged flowers (H&M); green tights (H&M); my sister's old green jacket; and a yellow polo I found in my closet that most likely used to be my sister's. The headband was red, and I wore it in the style like this" – next to a picture of herself in this glorious creation.

Since then, Tavi has pictured herself in any number of weird and wonderful guises. At one point, she is in her back garden, chin raised to the sky, lips pursed, in a brown Seventies-patterned polo neck and a pair of checked chef's trousers. And again, this time in military pose: black square sunglasses, a blue pom-pom attached to the left side of her head, with short pyjamas belted at the chest and brown leather suffragette boots.

She has also continued to offer an unedited stream of consciousness, allowing her audience to watch her grow from a child into a teenager – through the bad times: "My classmates called me a hippie. One kid said I should be 'in a basement smoking a joint'. I try not let these things get under my skin, though", and the good: "I'm getting a cell phone (yesss) and Nylon subscription (joy!) for my birthday".

And it seems that there is no stopping the numbers of people logging on to monitor her progress at tavi-thenewgirlintown.blogspot.com. Today, Tavi has some four million regular readers, plus fans in high places. Log on and you'll find pages of posts from last month's New York Fashion Week, where Tavi was a special guest in the front row at Marc Jacobs' show. Here she is snuggling up to the designer Alexander Wang at an élite after-party. And there, giving an interview to Vogue online. All as a result of her bedroom blogging endeavours.

If further evidence of her new role as fashion's coolest poster child were needed, even the design legend Diane Von Furstenberg now has an advert on Tavi's page; next to this, there is a link to where fans can buy their very own Tavi T-shirt (for $37). Not yet convinced? Google Tavi Gevinson, and before you reach her blog, you'll find a plug for her forthcoming interview in the new issue of LOVE, Katie Grand's painfully cool fashion magazine. This comes a month after she appeared on the cover of the equally chic Pop magazine – a privilege usually reserved for superstars like Madonna and Kate Moss. Inside, there are 13 pages on Tavi, who is described by Dasha Zhukova, the magazine's editor-in-chief, as "intelligent, fashion savvy, and one of the coolest 13-year-olds I've ever had the pleasure of meeting".

In her interview, Zhukova comments that Tavi represents "a crop of young people that are emerging as new role models ... who inspire through their personal style. Young women like Tavi stand on the frontline." All of which may be true – yet some may still find it difficult to watch this tiny teenager fluttering away into the open arms of the fashion pack, without wondering whether this industry's front line is really a safe place for any 13-year-old to stand.