The search giant has stumbled lately, but its popular Q&A service shows that getting people to create their own content can really pay off.

There are a few clouds gathering around Yahoo these days. The Internet star’s delay in rolling out a crucial new advertising system sideswiped its stock price in July, and investors remain jittery about its prospects against Google, Microsoft, and other rivals.

But one ray of sunshine is beaming at the company’s Sunnyvale, Calif., headquarters: Yahoo Answers.

An online Q&A service, Yahoo Answers has become the second most popular Internet reference site after Wikipedia, according to Comscore. In June, Yahoo Answers attracted 12.3 million unique visitors, a 35 percent spike from the previous month. (For comparison, media sensation YouTube had 13.4 million visitors in June.) During the same period, 947,000 people clicked on Google Answers, down 4 percent from May.

The secret to Yahoo Answers’s success?