Ashton Kutcher taught Poshmark that second-hand high-end shopping is cutthroat

Secondhand fashion marketplace Poshmark has always aimed to sit at a crossroads between a shopping site and a social network.

The platform allows anyone to set up their own online store — though its emphasis is on women's designer brands — through which they can offer used clothes that appear in the Instagram-like feeds of their followers alongside wares from brands and boutiques.

But the company recently encountered a problem familiar to many fast-growing social media sites: A user backlash over how the feed was being ordered.

The trouble started when Poshmark's first bona fide celebrity, Ashton Kutcher, opened a "closet" last year. Everything he posted would sell out within three to four minutes, and users started complaining that they never got a chance to view the goods before they disappeared.

"The community was really up in arms, saying why were they not notified," says Poshmark founder and CEO Manish Chandra.

The company responded with a new feature aimed at bringing more visibility between seller and follower — a broadcasting option called Posh Now that pushes every new item to the top of a follower's list in real time as they are posted.

Chandra said beyond the Kutcher incident, the change was necessary because of the service's massive growth in the past year. The company now claims to sport 5 million new items per day and 2.5 million sellers. It also boasts that one out of every one hundred fashion items bought by women in the United States is now resold through the site.

That growth is important because Poshmark is operating in a crowded space. Competitors like Letgo, Facebook Marketplace and OfferUp are all looking to be the new eBay or Craigslist for smartphone-focused millennials.

But Chandra insists that the new feature will offer a real-time shopping experience that none of Poshmark's rivals can currently match.

The company is now focused on pouring the plentiful data it has collected on its users' shopping habits into an algorithm that will help sellers better recommend items and personalize their feeds for their followers. Chandra said the update should be coming in the next few months.

"One of the things we have is massive, massive amounts of data," Chandra said. "We want to use the power of this data to build an experience that shoppers just can't get anywhere else in the online world."