Mariners general manager Jack Zduriencik said the hires will enhance director of professional scouting Carmen Fusco's staff.
"These new additions to the professional scouting department are excellent baseball minds who have a very unique understanding of the game," Zduriencik said in a club release. "They all have an incredible passion for the game and a continued desire to learn and improve. They bring a sense of confidence and a work ethic that will not be matched."
Stearns, 58, had an 11-year Major League career that included four All-Star appearances with the Mets, and he followed that with scouting roles and Minor League managing roles, most recently with the Nationals (2006-09).
Greene, 38, also played 11 seasons in the Majors with six different clubs, finishing with the Giants in 2006. He served as a scout for the Padres in 2008 and served as the quality assurance coach for the Rays last season.
Masse, 43, had a seven-year Minor League career and served as the hitting coach for the Mets' Double-A affiliate in Binghamton in 2009. He has managed and coached in the Minor Leagues since 1997.
John Schlegel is a national reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.