Facebook Inc.’s internal probe into potential misuse of user data is hitting fundamental roadblocks: The company can’t track where much of the data went after it left the platform or figure out where it is now.
Three months after CEO Mark Zuckerberg pledged to investigate all apps that had access to large amounts of Facebook data, the company is still combing its system to locate the developers behind those products and find out how they used the information between 2007 and 2015, when the company officially cut data access...