Italian luxury design house Prada has issued additional shares to boost its Hong Kong initial public offering to more than $2.46 billion, after a lacklustre trading debut last month. The family-controlled firm said in a statement late Sunday that the extra shares raised HK$2.5 billion ($321 million), after its highly anticipated IPO raised a lower-than-expected $2.14 billion. The so-called over-allotment option saw Prada issue 63.5 million shares at the IPO price of HK$39.50, which was at the lower end of its forecast range. Prada initially sold 423.2 million shares after floating 20 percent of its stock. Before the IPO, the brand had been 95 percent owned by the Prada family and executives. Since their weak June 24 trading debut, Prada shares have climbed above their IPO price, with the stock trading at HK$45 by the break Monday. Choppy global markets and concerns about the price of Prada shares weighed on the firm\'s debut, analysts said. The Italian group, which includes the Prada, Miu Miu, Church\'s and Car Shoe brands, is the latest high-end fashion brand to tap the huge Chinese market, the world\'s fastest-growing market for luxury goods. China is forecast to be the world\'s top buyer of products such as cosmetics, handbags, watches, shoes and clothes by 2015, according to consultancy PricewaterhouseCoopers.