VATICAN CITY — Pope Benedict XVI put church leaders on notice Thursday, saying social networking sites like ­Facebook and Twitter aren’t a virtual world they can ignore, but rather a very real world they must engage if they want to spread the faith to the next generation.

Benedict, 85, who tweets in nine languages, used his annual message on social communications to stress the potential of social media for the church as it struggles to keep followers and attract new ones amid religious apathy, competition from other churches, and scandals that have driven the faithful away.