Cathay Pacific has nonstop flights from LAX to Hong Kong for $468 and SFO to Hong Kong for $520 round trip. Departure dates are May, then mid-August to early December, then Jan-March 2019.
This fare sale is widely available on many dates with all alliances through Delta, Air Canada/United and Cathay Pacific for ticket prices in the $400s and low $500s.
Lowest fares close to $401-$417 round trip are available as Air Canada one-stop flights or Xiamen 2-stop flights.
Cathay Pacific Los Angeles LAX – Hong Kong HKG – LAX