The shadow hanging over Facebook since it filed to go public in February and looming larger in the lead-up to its IPO is its struggle to monetize mobile. The social network admitted as much in a regulatory filing in May, and CEO Mark Zuckerberg told investors then that beefing up Facebook’s mobile app was his top priority. That has extended companywide to the point that Facebook has decentralized its mobile team and seeded its members within other teams to ensure that all products are mobile-native, according to sources. Facebook declined to comment. Over the last month, Facebook has been stressing its mobile-first strategy in meetings with advertisers and agencies, sources said. With 488 million monthly active users on mobile…