Microsoft spokeswoman Crystal Duncan confirmed that Ryan left on Feb. 12. She would not comment on the specifics of his departure, but added that the company is actively seeking his replacement. Christopher Payne, vice president of MSN Search and Shopping and a member of the search-technology advancement team at Microsoft, has taken over Ryan's duties in the interim. "It's business as usual, his departure was unrelated to the company's emphasis on search technology," Duncan said. Ryan could not be immediately reached for comment. Microsoft is working at a furious clip to build a search empire to surpass innovations made by Google. It has invested heavily to develop a system that will allow people to search the Web, desktop applications such as Microsoft Word and e-mail, and the operating system. Much of it will debut through its next operating system, dubbed Longhorn.