'contributor in' is correct and can be used in written English.
For example: John was an important contributor in the project's success.
(I'm a contributor in the second group).
"Iran must be a contributor in the war against terror.
Van Horn has not been a consistent contributor in the last week, either.
There he was just another cricketer, a contributor in a team.
I met Wendell Steavenson, a recent New Yorker contributor, in Baghdad back in 2003.
The Rent Stabilization Association, a powerful trade group and major contributor in Albany, joined the fight.
"Remember me?" Croshere, a key contributor in the 2000 playoffs, said after the game.
But Goossens is just the most visible contributor in a noticeably inspired Fire side.
The prize honors a major contributor in traditional and classical architecture or historic preservation.
We're already the second largest contributor in terms of air strikes in Iraq".
While "Avatar" certainly helped, the film will probably be a larger contributor in the third quarter.
