Mountain View, Calif. -- Shares of Mountain View-based Google closed down more than 7% on Tuesday after the Internet search giant's CFO warned an investor conference that the company's growth is slowing. George Reyes said that Google will need to begin finding new ways to boost its revenue, triggering a sharp sell-off of the stock, which at one point was down 10%. "Growth is slowing and now largely organic. The search monetization gains have now largely been realized," Reyes told attendees of a Merrill Lynch conference in New York. "I'm not turning bearish at all. I think we've got a lot of growth a head of us," he said. "It's a question of what rate."