"Our vision is to make the world's daily habits inspiring and entertaining," she said in her first public appearance since taking the helm in July.
"Mobile represents not only a daily habit, but a platform shift we have to ride in order to be relevant."
Excluding $2.8bn (£1.7bn) earned from the sale of its shares in Chinese internet giant Alibaba, Yahoo!'s income was $177m (£110.5m) in the third quarter of this year.
Rather than invest in a different businesses strategy, Ms Mayer said Yahoo! would improve its performance by finding opportunities in its existing businesses, including internet search.
"We're committed to going back to our roots as a consumer internet company focused on user experience," she said, adding: "We intend to win."
But she said her top priority was to invest in the industry's transition to mobile devices - which even companies like Facebook and Google are struggling with.
"We do need more mobile engineers here," Ms Mayer admitted.
"It is clear that at some point in the future Yahoo! will have to be a predominately mobile company."
Ms Mayer is Yahoo!'s third boss in a year, after former boss Scott Thompson resigned less than six months at the top over a controversy about his academic credentials.
The company makes the majority of its money from advertising online, but has fallen behind rivals like Google in recent years, and missed out on the online social networking boom.
Yahoo! still gets around 700 million users visiting it every month, but the amount of time people spend on its websites is declining.
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