Spencer, who founded the business 11 years ago, has no current plans for the future and has decided to take a sabbatical to spend time with his family.
Macmichael joined Bluhalo, GyroHSR’s pure-play digital agency, as general manager in May 2010 from 20:20 (formerly GraphicoDMG) where he was director of business development.
Macmichael spent eight years at GraphicoDMG where he headed up work with clients including Pepsi UK and its sub brands, London Eye and Britvic. He was responsible for driving the agency’s digital strategy.
GyroHSR chief executive, Richard Glasson said: "Digital business accounts for over 40% of GyroHSR's worldwide revenues. It's an area that we continue to invest in, and in which we expect further strong growth. I'm delighted to welcome Alastair to the company".
GyroHSR acquired Bluhalo in March 2008 and its clients include Liverpool FC, Technicolor and Blackberry maker RIM.