Paytm's shares plunged as much as 28 per cent in a weak stock market debut on Thursday, a week after the country's biggest-ever initial public offering. The stock opened for trading at Rs 1,950 on the NSE, marking a decline of 9.3 per cent or Rs 200 from its issue price of Rs 2,150. Paytm shares extended losses after opening as the stock fell as much as 28 per cent, from issue price, to hit an intraday low of Rs 1,560.