BERLIN, Feb 4 (Reuters) - Shares in used-car trading platform AUTO1 rallied hard in their stock exchange debut on Thursday, as Germany’s first big initial public offering of the year was buoyed by insatiable investor demand for tech stocks. Shares opened 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 ($9.48 billion). (Reporting by Douglas Busvine Editing by Riham Alkousaa)