* Billboards, sports events to be bigger part of mix
* Marketing effort targets 18-to-34-year-olds
* Seeks to reverse drop in revenue, user engagement
* Still mulling future of 35 pct stake in Yahoo Japan
SAN FRANCISCO, May 14 (Reuters) - Yahoo Inc plans to ramp up advertising and marketing efforts as it seeks to break its reliance on an "aging demographic" and become more relevant among young adults, the company's finance chief said on Tuesday.
The struggling Web portal's brand will be more visible on outdoor billboards and at sporting events, among other places, as it seeks to woo 18-to-34-year-olds and get the word out about new products, CFO Ken Goldman said at the J.P. Morgan Global Technology, Media and Telecom conference in Boston on Tuesday.
"Part of it is going to be just visibility again in making ourselves cool, which we got away from for a couple of years," said Goldman.
He noted that the efforts will require spending to advertise across various mediums. Goldman gave no specifics on budget or expenditures.
Yahoo is trying to reverse a multi-year decline in revenue and user engagement on its website, amid competition from new social networking and mobile websites such as Facebook Inc and Twitter, and from search giant Google Inc.
"One of our challenges is we have had an aging demographic, if you will," said Goldman.
Marissa Mayer, who became Yahoo's chief executive in July, was one of Google's earliest employees and is respected in technology circles for her online product-design expertise. Since taking over, Mayer has launched new versions of key products, such as Yahoo's Web email and its Flickr photo sharing service, and acquired several small start-up companies.
Yahoo shares have surged roughly 70 percent since Mayer took over, though analysts say much of the rise is due to stock buybacks and the growing value of Yahoo's Asian assets.
Goldman hinted that Yahoo could buy back more shares once its current stock repurchase authorization is completed. He added, however, that any future buybacks would depend on the stock price.
"I do like the idea of buying back stock," he said. "So I don't necessarily suggest at all that the fact that we've got a little bit more to go on the existing purchase does not mean that we would not go beyond that and buy more."
Goldman said the company continues to explore the best course of action for its 35 percent stake in Yahoo Japan, including everything from working with the company more closely to potentially selling the stake. He described Yahoo's 2012 sale of half of its 40 percent stake in Chinese Internet company Alibaba Group as "unfortunate" and a result of Yahoo's unstable situation at the time.
Shares of Yahoo were up 1.4 percent at $26.75 on the Nasdaq at midday on Tuesday.