Shares of Stitch Fix lost almost a third of their value Tuesday after the company disclosed user data for its online personal styling service that disappointed investors.

The company said its "active" clients grew 25 percent from a year ago to 2.7 million by the end of its fourth quarter ended July 28. Analysts were expecting an even bigger bump to 2.81 million, according to data compiled by StreetAccount.

The disappointing news sent shares skidding 32.6 percent to $30.10 a share in midday trading. It was the stock's heaviest trading day since its IPO in November with more than 27 million shares trading hands by midday, compared with its 30-day average volume of 3.2 million shares, according to data compiled by FactSet.

To be sure, the stock is still up 17.4 percent so far this year, and CEO Katrina Lake told CNBC's "Squawk Alley" that revenue was on the high end of its previous guidance.

Stitch Fix, which provides a box of clothing delivered to your door however often you choose, was originally just for women and in the United States. The company is now expanding into men's and children's clothing, and is bringing the business across the pond to the United Kingdom.