Nick Robertson, the founder of British online fashion retailer ASOS, has stepped down as chief executive after 15 years in which he transformed the internet minnow into a retail powerhouse with fans around the world.

ASOS, popular with Internet savvy twentysomethings and high-profile fans such as British singer Rita Ora and US First Lady Michelle Obama, said on Wednesday that Mr Robertson would remain at the firm as a non-executive director.

He will be replaced at the top by Nick Beighton, the company's chief operating officer, with immediate effect. Beighton joined ASOS in 2009 as chief financial officer, stepping up to the COO role last October.

“I’d like to acknowledge Nick Robertson’s extraordinary achievement. His passion and vision have built a start-up into a world class company,” said ASOS chairman Brian McBride.

Until last year, when it issued three profit warnings due to currency swings and higher investment needs, ASOS, with Mr Robertson the driving force, had been the success story of the British retail sector and a darling of the stock market.

Robertson and Quentin Griffiths founded the-then As Seen On Screen in 2000 and floated the firm on London's Alternative Investment Market at 20 pence in 2001.

The shares hit a high of £71.95 in February 2014 before the first of the warnings. The stock closed at £29.84 on Tuesday, valuing the business at £2.5 billion.

ASOS had a tough 2014 when it was hurt by the negative impact of exchange rate movements and a fire at its main warehouse. However, its shares have risen 16 per cent so far in 2015 as it has recovered. Last month it raised its full-year profit guidance after a strong third quarter.

Mr Robertson owns 8.4 per cent of its equity, according to Reuters data.

Reuters