SAN FRANCISCO — Last month the U.S. Securities and Exchange Commission announced an enforcement action against Sand Hill Exchange, a Silicon Valley startup running a website where investors could bet on the fates of hot private tech companies much like playing in a fantasy sports league.

It was a seemingly small case—the two-month-old exchange had taken in only about $3,000 and was fined $20,000. But just two days after announcing the bust, the SEC sent a panel of three enforcement lawyers, including two from Washington, D.C., headquarters, to discuss it with local securities lawyers at Sidley Austin’s San Francisco office.