Facebook is ramping up efforts to entice companies such as Delta Air Lines and J.C. Penney to sell wares on its pages and convert more of its 500 million users into online shoppers. Managers at the Palo Alto (Calif.)-based social network have met in the past month with more than 20 companies, said David Fisch, who runs a newly formed commerce partnerships group at Facebook. The aim is to help retailers set up shop on its pages and build tools that let Web users interact while buying.