(Adds CEO interview, context on investors) BERLIN, Feb 4 (Reuters) - Shares in used-car trading platform AUTO1 raced ahead in their stock exchange debut on Thursday, as Germany’s first big initial public offering of the year was snapped up by tech-hungry investors. The shares opened in Frankfurt at 55 euros a share - 45% above the price at which they were sold to investors in an oversubscribed offering that valued the nine-year-old Berlin startup at 7.9 billion euros ($9.47 billion). “We’re mega-happy with how it has gone,” CEO Christian Bertermann told Reuters in an interview. “It shows how much confidence we’ve built up among existing and new investors with our business plan: there is a better way to buy a car and that is online.” AUTO1 priced its 1.8 billion euro initial public offering (IPO) at the top of a 32 to 38 euros per share range, following strong demand from investors in Europe’s second big tech IPO of the year. After popping at the open, shares drifted back to around 51 euros, putting a market value of around 10.6 billion euros on the business. SCALING UP AUTO1, the top platform for buying and selling in Europe’s 600-billion-euro market for used cars, will reap 1 billion euros from the sale of new shares, most of which will be ploughed into building its Autohero retail brand. Autohero sales grew by 75% in the fourth quarter of 2020 from the preceding three months, Bertermann said, as the direct-to-consumer brand outgrew AUTO1’s larger platform for dealers in percentage terms. Existing backer Softbank’s Vision Fund, which owned a 20% stake, will turn a big profit by selling shares, having backed AUTO1 in early 2018 at a valuation of 2.9 billion euros. DN Capital, which first backed AUTO1 in 2013, hailed the flotation as the result of co-founders Bertermann and Hakan Koc’s “brilliant execution and clear-sightedness” in building a business than now spans 30 countries. New investors, including U.S. venture fund Sequoia and hedge fund Lone Pine were so-called ‘cornerstone’ investors in the IPO to the tune of 150 million euros each. Bertermann noted, however, that the overall order book was dominated by European money - the largest single allocation went to a German investor whom he declined to identify. The Frankfurt listing cements its status as one of the two leading venues for tech stocks on the European continent. A recent Deutsche Boerse report said it accounted for 26% of tech market capitalisation behind Euronext Amsterdam on 27%. Last week, $12 billion euro Polish firm InPost jumped on its Euronext debut, as did $5 billion boot brand Dr. Martens and $1.63 billion greeting card retailer Moonpig in London. Goldman Sachs, Citi, Deutsche Bank and BNP Paribas organised the AUTO1 IPO as global coordinators, with the help of Barclays, HSBC, Numis, RBC, Credit Agricole, Commerzbank , Mizuho and Wells Fargo. ($1 = 0.8340 euros) (Additional reporting by Arno Schuetze Editing by Riham Alkousaa and Jane Merriman)