The town is working on finalizing a contract with an architect group to lead the design process for the $4.2 million youth center project. Boston-based CBT Architects and Andover-based Rob Bramhall Architects, Inc., which applied in partnership, were selected among three finalists, narrowed down from a total of five applicants, by the Youth Center Building Committee. Once a contract is finalized, the design process can begin for the 20,000-square-foot youth center to be located behind Doherty Middle School, said Maria Maggio, the town’s plant and facilities director. Voters at a Special Town Meeting in December approved spending $2 million from the town’s operating budget to fund part of the project. The Andover Youth Foundation is continuing its fund-raising efforts with the private sector to supplement $3.8 million in donations it already has collected, said chairwoman Diane Costagliola. The foundation expects to kick off the first of a series of upcoming fund-raisers during the Andover Days event Sept. 15. Costagliola said the project is still on track for a June 2013 groundbreaking.