On Wednesday, shares of Snap Inc. were priced at $17. The price values the California company at $24 billion. The offering is the most high-profile tech IPO in years and represents an important milestone for the five-year-old Los Angeles startup. One of the main challenges for Snap is the deceleration in user growth. Snap said its biggest revenue opportunity is the growing budget for worldwide mobile advertising, which could reach $196 billion by 2020 from $66 billion currently. Snap’s shares are set to trade on the New York Stock Exchange on Thursday.