 Shares of Zendesk Inc. ZEN, -6.92 dove 5.6 toward a two-year low in premarket trading Thursday, after the customer-service software company said it decided not to pursue a sale, as no actionable buyout proposals were received. The company said as part of a strategic review to enhance shareholder value, the company reached out to 26 potential buyers and partners, including 16 potential strategic partners and 10 financial sponsors and a group of investors who had previously expressed interest in a purchase. 