Yahoo Inc. announced that it will boost its stock buyback plan by $5 billion, which will return more cash to shareholders as it seeks to revive growth. The largest U.S. internet portal will sell $1 billion in convertible debt maturing in 2018. The companies CEO Marissa Mayer's turnaround has focused mainly on acquisitions of smaller tech companies in order to reach new users. Last year Yahoo sold half of its stake in Alibaba Group Holding Ltd. and plans to return most of the $3.65 billion in proceeds to shareholders.