Why are YouTube stars so popular?

With millions of subscribers, top YouTubers such as Zoella have huge, passionate audiences. Here's a handy guide to help you understand their popularity

British vlogger Zoella has just reached the milestone of 10m subscribers to her main YouTube channel, but she has a long way to go to catch its most popular creator PewDiePie, who is about to pass 42m.

They're just two of the most prominent YouTube stars. In October 2015, online-video tracking firm Tubular Labs reported that there were more than 17,000 YouTube channels with more than 100,000 subscribers, and nearly 1,500 with more than 1m.