Holtznagel, who placed third in the 2011 season of Australia's Next Top Model, caught the attention of Guess founder Paul Marciano with her plethora of selfies and portfolio of campaigns for brands such as Cotton On.

"That's SIMONE!! I was talking about that I found on Instagram from Australia! She is 21 and now moved to Cal. [California]," Marciano posted to his 25,000 followers.

The blonde stunner has the body of Sports Illustrated star Kate Upton and the bone structure of fellow Australian model Nicole Trunfio. She will star in a number of the brand's future campaigns.

Last year, Guess conducted a similar casting call via social media. The winner was chosen by popular vote on Facebook.

Holtznagel moved to the US this year following the death of her "adopted mum" and mentor Charlotte Dawson.

On the eve of her 21st birthday she posted a photo of herself and Dawson to commemorate their relationship.

"She's been with me all day, spoiling me every year since my 18th. Wishing you could celebrate with me tomorrow (and every other day/birthday) Mama but I'll be sure I have a chard [Chardonnay] for you," she wrote.

The model, who grew up in Wollongong, is also a budding actress and after speaking with a Texan accent for 7-days last year she auditioned for the starring role in an Anna Nicole Smith biopic.

"It was sad because I got so into the role of playing her and had my heart set on it then I didn't get it. I still remember most of my lines. It was my first massive audition and I was one of the only gals in Australia they wanted to see, so that was nice to know. I know it would have been a long shot for little old me to get it," she said after missing out.