Johnny Won, mobile and gaming platforms manager at Hill Holliday, is leaving the IPG unit to launch a start-up focused on local mobile search with Zach Taylor, formerly a creative technologist at McGarryBowen. Won, who wraps up this week at Hill Holliday, offered few details about his next venture, but suggested there's plenty of room for improvement in local search. He plans to build prototypes for a local mobile search service with Taylor to attract angel funding. This year, under his leadership of the mobile and gaming practice at Hill Holliday, the agency won Adweek's Media Plan of the Year for Branded Entertainment for a promotion integrating Dunkin' Donuts with The Sims Social. Last year, it won Adweek's Media Plan of…