The model and the designer are close friends and will head up a team called Step Forward to complete a 6.2-mile sponsored AIDS Walk around New York this Saturday (19.05.12). They are currently taking sponsorships to reach their target.
Kloss told vogue.co.uk: ''The idea came about at the Met Ball with a mutual friend of ours.
''We were in a sea of glamour and we looked at each other and said, 'what do we do next?'
''The AIDS Walk became a perfect opportunity to change our ballgown and black tie for sneakers and work-out clothes.
''Juicy Couture is even donating a bucket of money for me to wear their clothes for the event which is amazing - it's fantastic to see my friends in The Fashion community getting behind us, come on guys!''
Karlie, 19, wore a custom-made Pink gown by Jason to the Met ball earlier this month. She joked she had been training for the walk by getting plenty of practice on catwalks.
She said: ''I have been training for this walk on many catwalks around the world.
''I wanted a day to spend with my friends in New York that was healthy and positive and what a better way to do that than in Central Park and raising awareness for a cause that I am passionate about. It's about raising awareness and making a difference.''
The former ballerina also said she was inspired to do the walk after a moving story she had heard.
She added: ''I sat at the Glamour Women Of The Year Awards one year and was inspired by a woman called Elizabeth Glaser and her son Jake and their story.
''It was through this I became involved in awareness for Paediatric AIDS. My father is a doctor so I understand the fight as well.''