Asos’ profit before tax surged 18% to £27.2m in the half year to February 28, 2013, as it reaches six million customers worldwide.

In the period, retail sales soared 34% to £352m driven by international sales, which were up 39% to £214m. UK sales also increased 26% to £137m.

However, retail gross margin was down by 60 bps and gross margin declined by 90 bps.

Asos chief executive Nick Robertson said the performance was “strong” after the retailer has invested in price, quality, enhanced delivery options, marketing initiatives as well as placing teams in international territories and improving its international and mobile websites.

He added: “We are already seeing the benefits of this investment across all territories with increased customer awareness, increased shopper frequency, higher conversion rates, more items per basket and strong sales growth. At the same time we have reached the milestone of six million active customers worldwide.”

He said progress on its Russia and China sites remains “on track”, as Asos plans to launch in Russia next month, while it aims to open in China at the beginning of the new financial year.

Robertson said: “Momentum is strong, and we remain positive in our outlook for 2012/13 as we continue our journey to becoming the number one online fashion destination for twenty-somethings, globally. Our international roll-out continues and our £1bn sales ambition for the group is firmly in our sights.”

Today Asos also revealed it is putting in place a new ‘Long Term Incentive Plan’ to incentivise the senior management team to deliver the planned growth at the retailer.

In the period, Asos said it invested in “the first price right price” approach to reduce markdowns in the half year. Asos, which is rataionalising its supplier base, is also establishing a dedicated sourcing team to “drive retail gross margin efficiency” and reduce lead times.

Since the end of the period, Asos has improved its English mobile site to take advantage of the 30% of traffic from mobile devices. It is now refreshing its iPad and iPhone apps and introducing an Android app as it continues to open international sites.