SAN FRANCISCO — Yahoo Inc. is jumping on the Twitter bandwagon in its latest attempt to get people to use its Internet search engine more frequently. Beginning Thursday, Yahoo will mine the short messages posted on Twitter to find fresher information about hot topics. Microsoft Corp. and Google Inc. had earlier announced plans to incorporate Twitter messages into search results, but Yahoo said it will be the first among them to include such "tweets" on its main search results. The addition comes at a pivotal time for Yahoo.