SAN FRANCISCO — Pinterest on Wednesday priced its shares at $19 each for its initial public offering, in a sign of healthy demand by investors after the appetite for fast-growing but money-losing tech companies appeared to be on the wane. The price valued the digital pin board company, which lets people save images and links from around the web, at $12.7 billion. That is a little above its last private fund-raising round, which had pegged the company at $12 billion. By selling at $19 a share, Pinterest raised $1.6 billion from big investors in the offering.