San Francisco to Hong Kong on United Airlines is as low as $547 (K class) for flight departures in April 2015 with nonstop outbound flight on United and inbound via Shanghai on DragonAir with United Airlines from Shanghai PVG to San Francisco SFO.
You can book nonstop flights both ways with United Airlines for $683 roundtrip.
These low rates are available for a couple of dates in May and for about $100 more. Most dates in May have fares at $1,000 or over.
Korean Air SFO-HKG via Seoul, South Korea $566 April 2015 dates
Skyteam has a comparable fare that features four segments on Korean Air with an overnight in Seoul, South Korea on the outbound from 6:15pm arrival to 1:40pm departure for Hong Kong the next day. I view this as a chance to visit Seoul and Hong Kong on one deeply discounted economy class ticket.
You can also route an itinerary without an overnight in Seoul for same price.
$566 Orbitz.com fare: Korean Air SFO-HKG via ICN Monday April 27 – Wednesday April 29 to May 6, 2015. Lowest fares are last week in April.
You won’t earn many miles on these fares in 2015 Mileage Plus and SkyMiles, but at these fares, saving dollars now might be favorable to earning miles for later.
These flights are easy to find using Google Flights for SFO-HKG.