The Christmas holiday brings peak attendance for most churches, and an increasing number of U.S. religious groups are using the boom time to wow parishioners with virtual choirs on YouTube and Instagram advent calendars. More than 500 churches will stream Christmas sermons online this year, up from just a handful in 2007, said DJ Chuang, host of the Social Media Church, a podcast with church leaders about social media. They use it to tell the stories of the church. The online churches appeal to those who have moved away from their own parish, people who may be reticent to walk into an actual church and people who wish to attend a service outside normal times. The New Jersey-based Liquid Church has had an online pastor since 2009, and took to YouTube last Christmas to share a virtual choir using videos from roughly 500 church members who attend services remotely.