Michelle Phan has been the reigning queen of YouTube beauty for years, leading to her own makeup brand via L'Oreal (Em) and her own beauty products sample subscription service (Ipsy), among many other things. But in yet another sign that social-media stardom can be short lived, Ms. Phan, 28, has been eclipsed not just once but twice by up-and-coming beauty bloggers for monthly views, according to a new report by video analytics firm Pixability.

Bethany Mota (macbarbie07), 19, actually surpassed Ms. Phan for monthly views for the first time in late 2013 and has kept growing since. An even faster riser, Zoe Sugg (zoella280390), 25, surpassed Ms. Phan for monthly views in February, and Ms. Mota this spring, according to the Pixability data. Both Ms. Mota and Ms. Sugg now top Ms. Phan for subscribers as well.

With nearly 1.2 billion lifetime views, Ms. Phan still tops both Ms. Mota (682 million) and Ms. Sugg (433 million). But things are changing fast. Ms. Sugg hit 28 million monthly views last month, surpassing the all-time category record of 26 million Ms. Phan set in 2009 with her "How to Get Lady Gaga's Eyes" videos.

She's been a rock star herself ever since. The next year, she signed her first endorsement deal with L'Oreal's Lancome, followed by the launch of Ipsy in 2012 and the For All Women Network (FAWN) on YouTube, which ironically helped launch Ms. Mota's career.

Then, in 2013, came Em by Michelle Phan cosmetics, followed last fall by a music label and book, Make Up: Your Life Guide to Beauty, Style, and Success -- Online and Off. This year, Ms. Phan also helped launch a talent network – Icon -- and earlier this month Ipsy Open Studios, a space in Santa Monica for beauty entrepreneurs.

All that has been taking time away from Ms. Phan's YouTube beauty channel, said Pixability Chief Technology Officer Andreas Goeldi, and it shows.

"Her channel has been publishing with less frequency," he said. "We see twice a week as the best practice for frequency, because it's what a lot of viewers expect from you." Ms. Phan has been publishing more like twice a month as of late.

The universe of YouTube beauty bloggers is changing too, Mr. Goeldi said, "with younger stars who speak to more focused target audiences, say younger teens or certain ethnic groups, or people specifically interested in hair."

Ms. Phan has more of a broad appeal and "traditional approach," he said. "If you look at her current videos, it's always highly produced, extremely professional but also very traditional. If you look at younger talent that's been growing very quickly like Zoella [Zoe Sugg] in the U.K., she's still typical YouTube, with a lot of collaboration with YouTube stars, which I think just gives her higher credibility with a younger audience on YouTube."