Hong Kong was one of the last markets in the world not to be Google dominated. As recently as 2012, the South China Morning Post declared "Yahoo is still HK's top search engine". Today Yahoo has a 12% search engine market share.
While Experian HitWise data shows Yahoo was more popular than Google until 2013, data from StatCounter shows Google surpassed Yahoo in Hong Kong in 2009.
While Google has the ability to send you more traffic than Yahoo, if you're already advertising on Google at full steam, you could expand your potential audience by advertising on Yahoo too.
Since the ad systems of both search engines are fairly similar, you don't have to start over optimizing your account from scratch. You can clone your already high performing AdWords account over to Yahoo.
Yahoo.com.hk is a Chinese only website. In 2004, the English version was shut down due to low usage. If you're looking to expand your reach among Chinese speakers in Hong Kong, Yahoo can deliver.
Since there's less people searching on Yahoo, the searches are in Chinese only, and opening an ad account is more onerous than Google, the bids on Yahoo are about 10-30% less expensive than Google.
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