HongKong-Tokyo-Seoul flights
 

Are there any airlines that service these three cities? I need to go from HK to Tokyo, to Seoul, and back to HK.
I have been on several airline websites (Korean Air, JAL, Cathay Pacific) but they don't allow for mutiple city reservations. Any suggestions? Thanks.

Look at kayak.com and use multi citi option.

Are you sure? I checked CX's website, and there's a link for "Multi-city/Stopover" link in the bottom of the reservations box. I'm sure most airlines have some of the same on their websites.

Having said that, no single airline serves all of those 3 markets non-stop. Apparently, Korean airlines (KE, OZ, etc) will have Seoul-Tokyo and Seoul-HKG; Japanese ones will have Tokyo-Seoul and Tokyo-HKG; and HK ones will have HKG-ICN and HKG-Tokyo.

I went on each airlines website and they would only allow me to book their (2) legs. Then I would need to book a oneway for the third leg. Expensive.
I called CP and KAL and the agent could book it for me but said it would be more expensive, which it was.
So I went to American Airlines since CP and JAL are partner airlines and I'm a platinum member. The American agent was able to book the trip using CP and JAL and it was much less! Crazy but true.
Kayak did offer many options but the non-stops above worked out best. I like the Kayak site though. Thanks for the help.

Not crazy. AA's site offers many more partners and even non-partners' flights for sale, making it basically an online travel agent. That's not the case for most airlines' sites.

You probably could have booked the same using Orbitz or Expedia, etc.

So, now I understand the original point in your original post. It wasn't that those airlines' sites don't offer multi-leg or multi-destination booking, it was that they don't offer other airlines' flights in markets they don't serve.