It was a result of America's reaction to the GFC and for Karp it was the start of a downward spiral.
She gave up the lease on her beach shack and moved in with her mentally ill mother, who later kicked her out.
She couldn't stay with friends - they had problems of their own - and without a job and with only a small amount of money she couldn't sign another rental lease.
When her biological father, whom she barely knew, took his own life she inherited a truck and caravan. So began Karp's journey as a homeless person.
Without electricity she cooked her meals on the truck's engine or bought ready-to-eat 99-cent food.
She showered at a local gym after taking advantage of a $9.95-a-month gym membership and every morning she would buy a coffee from a nearby Starbucks so she could use their free wifi to search for jobs online, 10 hours a day.
Karp, who became homeless a week before her 24th birthday in 2009, admits she was scared.
"The word homeless has such a stigma to it. It's not something you really think about until it's actually happening to you and it crosses your radar, and I had no idea what I was doing ..." she tells AAP from the US.
"On some level I also thought, or hoped, that it would be a very short-term thing; maybe for two weeks or something until I could find another job and get back on my feet."
Karp, who admits she was in denial about the recession, was homeless for two-and-a-half years.
During that time she was determined to dress as she normally would have so she didn't look like the stereotypical homeless person.
"Because there's such a stigma to it you don't want to come across as homeless, because who's going to offer you a job if you look homeless, who's going to give you a shot?"
With just $300 in her pocket, Karp needed to find work quickly but so did many other Americans.
She was willing to take anything, she says, but was caught in a Catch-22.
There were very few jobs in her field of corporate marketing while potential employers, at a petrol station for example, had no desire to hire someone they thought would later leave for a better position.
Being repeatedly told she was overqualified for positions was frustrating.
Meantime, she had to battle bureaucracy for government unemployment benefits.
For many months, Karp would go without these basic hand-outs because the department was either sending her cheques to the wrong address or was overwhelmed with the increase in beneficiaries.
While all of this was happening, Karp was blogging about being homeless, after a friend suggested she do so.
"So I did the first one as a joke and then it felt really good and it felt cathartic and so I kept doing it," she says.
"And it was more like a journal or an online diary, or something where my friends could check up on me and see how I was doing, but it was anonymous and I didn't expect people to start reading it."
She used the free Starbucks wifi to post blogs every few days and she soon had followers.
After nine months of living at the Walmart car park, however, the budget shopping empire tried to have her trailer towed.
At about the same time CNN heard about her story and wanted to cover it.
Afterwards she received more attention and her blog followers continued to grow. She was soon offered book deals and had to decide whether she wanted to put her name and face in the public eye.
"I had turned down some literary agents that had approached me earlier because I didn't think that I could do it and I also knew that it would mean talking about some of the more negative aspects of my childhood and my family," she says.
Karp is referring to the verbal, physical and sexual abuse she had experienced as a child, and talking about her mother suffering from bipolar disorder.
"At that time I was still holding out hope that maybe there could potentially be reconciliation down the line," adds Karp, who hasn't heard from her mother since becoming homeless.
In October 2009 Karp signed a book deal that saw her spending the following year-and-a-half writing her story.
Although she was homeless the entire time, her situation was starting to look up.
In about August 2011 Karp moved into a rental apartment, and for a year now she has had paid employment, working as a marketing assistant for a theatre.
She earns up to $20,000 a year less than she used to but says the job is wonderful.
"You can't complain because it's a job, it's something, and here in the US nobody can complain - when you've got a job you're one of the lucky ones."
Now, in her spare time, Karp travels the US promoting her memoir, The Girl's Guide to Homelessness, and giving talks at homeless shelters.
She has also co-founded World Homeless Day, which is into its second year.
Since experiencing homelessness, Karp's outlook on the downtrodden has changed.
"Every single homeless person has a story and the reasons for homelessness are as varied as the homeless people ..." she says.
"I now believe that every homeless person deserves help, even if they do have a drug problem or are mentally ill, they need help."
Despite her traumatic upbringing and recent experiences, Karp is remaining positive about the future.
She still dreams about buying a home but for now is content with renting and readjusting to her new lifestyle.
"It's just good to be in a place again; it's a relief and it's kind of surreal.
"It feels very strange having a bed again or a yard for my dog and kind of feeling secure (but) I'm just happy to have an apartment. It's just a little studio apartment, but it's a place to call my own. What more can I ask for right now really?"
* The Girl's Guide to Homelessness by Brianna Karp is published by MIRA (RRP $29.99)
- AAP
