Over the past few years, as a slew of web video subscription services have rolled out, doubts have arisen over whether young people will pay for content of the sort that seems widely available for free online.

YouTube Red appears to still be finding its audience, while the startup Vessel, which promised early access to popular web video series, sold to Verizon only to be shuttered (Verizon did retained much of the team behind Vessel to work on other projects).

With that backdrop, the report card of digital entertainment company Rooster Teeth looks impressive. The company says it has crossed the 200,000 subscriber threshold, doubling its paying user base over the past year.

Rooster Teeth specializes in making content for young, web-savvy entertainment fans--i.e., people who are really into gaming, animation, and science fiction. The company, which has been around since 2003, was acquired in 2014 by Fullscreen Media, which itself is part of Otter Media, a joint venture between AT&T and Chernin Group.

Though Rooster Teeth has a very healthy free, ad-supported business (it boasts of 28 million YouTube subscribers across multiple channels), it has been experimenting with digital pay models for over a decade. In the early days, fans who paid around $20 a year were called “sponsors” and would get early access to the long-running video-game-inspired series “Red vs. Blue,” as well as copies of DVDs. Most of that consumption happened on Rooster Teeth’s desktop site.

Starting last the summer, the company evolved this product to become a full-fledged subscription video-on-demand service, over time adding more distribution outlets (including connected TV apps last month on Apple TV and Xbox One). Rooster Teeth also ramped up its original entertainment output, providing subscribers with exclusive access to series like the scripted comedy “Crunch Time.”

To be sure, even as Rooster Teeth’s subscription business shows early signs of success, the marketplace only grows more crowded. Not only are there a slew of niche offerings, such as NBCUniversal’s comedy-focused Seeso as well as Fullscreen’s own web video subscription products, but there are also a flurry of more robust, skinny TV bundles including AT&T’s DirecTV Now.

Currently, there are two subscription options. Rooster Teeth “First” starts at $4.99 per month and offers fans early access to shows and tickets to live events, discounts on merchandise and an ad-free experience. Then there’s “Double Gold,” which starts at $34.99 per month and includes all of the First perks plus a monthly subscription “box” of merchandise valued at $60.

“Once these things start rolling they gather momentum,” said Matt Hullum, Rooster Teeth’s chief executive.

The key to Rooster Teeth’s paywall success has been treating subscribers like club members, said Mr. Hullum.

“We try to do a big show every quarter, and our content is not like anywhere else,” he said. Most Rooster Teeth shows, like its popular anime fantasy series “RWBY, ”do eventually make it to the company’s website and YouTube channel, where they can be viewed for free along with lots of shorts, animated clips and pop culture-centric talk shows. Yet some of the bigger projects like the futuristic scripted show “Day 5” are for paying customers only.

“We’ve tried to be mindful of having a consistent drumbeat of new content for the service,” said Mr. Hullum.

Besides making money from ads and subscriptions, Rooster Teeth also hosts events like the Comic-con-esque “RTX.” And as Mr. Hullum said, merchandise is a key revenue driver for Rooster Teeth. That includes hats and toys tied to its series, as well as holiday ornaments and $77 adult onesies.

Getting people to pay for merchandise and content is “how we made our first dollar at the company,” said Burnie Burns, Rooster Teeth’s chief creative officer. “We’re not trying to make a pivot here. We want to scale something that already works.”

Write to Mike Shields at mike.shields@wsj.com