Yahoo! Inc., the largest U.S. Web portal, is paying about $30 million to buy Summly, a mobile startup run by a 17-year-old, according to a person familiar with the transaction.

Yahoo announced the deal yesterday on its blog without disclosing terms. Summly, founded by Nick D’Aloisio at his London home when he was 15 years old, is a mobile application that summarizes news articles for small-screen devices. He’ll join Yahoo along with some members of his team, according to the statement.

Chief Executive Officer Marissa Mayer is focusing Sunnyvale, California-based Yahoo on providing Web services that are customized for individual users, and aims to add engineers by buying small technology startups, she said on a conference call last year. Yahoo has acquired at least six such teams -- including Jybe Inc., Stamped Inc., OntheAir, and Alike - - since Mayer took over in July.

“Yahoo in my mind is one of these classic Internet companies and there is so much opportunity now that they have new leadership with Marissa Mayer,” D’Aloisio said in an interview. “There’s a massive opportunity in what they’re doing, which is taking technologies like Summly and allowing them to become used by hundreds of millions of people.”

Sara Gorman, a spokeswoman for Yahoo, declined to comment on the price.

“Most articles and Web pages were formatted for browsing with mouse clicks,” Yahoo said on the blog. “The ability to skim them on a phone or a tablet can be a real challenge. We want easier ways to identify what’s important to us.”

Personal, Mobile

Mayer has said she sees the company building sites and technologies for daily activities such as checking e-mail and stock tickers. In January, she said she’s focused on technology that will personalize content from the Web and deliver it to people on their handheld devices.

“We think about how do we take the Internet and order it for you,” Mayer said.

Yahoo gained less than 1 percent to $23.38 at yesterday’s close in New York, leaving the shares up 17 percent this year. In German trading today, the stock fell 1 percent to the equivalent of $23.45 at 10:28 a.m. in Frankfurt.