Thank you, Chris. And thank you all for joining us on Spark Networks second quarter 2021 conference call today.
As a reminder, Spark ambition is to become the leading social dating platform for meaningful relationships. We own and operate a strong portfolio of brands, the five largest being Zoosk, SilverSingles, EliteSingles, Christian Mingle, and Jdate.
Our primary focus is on the 40 plus demographic and the religious space segment, a market we estimate to be around $2.3 billion in revenue and growing at 7% per year. Along with Match Group, Bumble and ParshipMeet, we are one of the four scaled online dating companies. Every quarter, we register more than 3 million users and have more than 870,000 paying subscribers in our properties.
While we have presence in many countries, 90 plus percent of our revenue is in the U.S., Canada, U.K., Australia and France. And most of our focus is growing our U.S. based business.
Before going any further, I would like to welcome our new Chief Financial Officer, David Clark, who is with us on our call today. David officially joined us last week, and this is his first Spark earnings call. He brings more than 20 years of public market experience most notably serving as CFO of the Meet Group, now a subsidiary of ParshipMeet Group, a leading provider of live streaming video experiences and interactive dating solutions.
We also recently appointed Bangaly Kaba and Joseph Whitters to serve on our Board of Directors. These new Board members bring relevant product and public market expertise to the company. Mr. Kaba has extensive experience in consumer technology, building mobile digital products, and accelerating growth through social media. Notably, Mr. Kaba helped grow Instagram from 400 million to a billion monthly active users as head of growth and design and built instacart core product functionality. Mr. Whitters has expertise in accounting, governance, finance, risk management, and more than 20 years of experience in public markets driving shareholder value for investors.
Turning now to Q2 results, revenue for the second quarter of 2021 was $55.3 million, a decrease of $1.2 million compared to $56.5 million in the second quarter of 2020.
Our four largest legacy Spark brands SilverSingles, EliteSingles, Christian Mingle and Jdate collectively grew by 10% year-over-year. The decrease in overall revenue was attributable to the 3% decrease in the number of average paying subscribers specifically driven by risk. Adjusted EBITDA was $8.3 million in the second quarter of 2021, a decrease of $1.8 million compared to the $10.1 million in the second quarter of 2020.
Turning to our key performance indicators. Spark's monthly average revenue per user or monthly ARPU increased to $20.96 in the second quarter of 2021 compared to $20.81 in the same period of 2020 or average paying subscribers decreased by 26,798 or 3% to 878,618 in the second quarter of 2021 compared to 905,416 in the same period of 2020. Overall we are seeing healthy growth in our Spark core asset Silver, Elite, Christian Mingle and Jdate and a decline in Zoosk revenue.
For Spark's core assets, we are seeing good growth in the older demographic and higher engagement in our religious properties thanks to improvements in or matching algorithms.
For Zoosk, while we are in the right path to turn it around, and have reduced its top line decline from 15% to high single-digit, its performance in Q2 was a bit below expectations. This is mostly due to stricter fraud access controls, and the delay in product revenue initiatives. The overall rise in cyberattacks since the pandemic required us to tighten fraud controls more aggressively on Zoosk, which we believe led to lower than expected engagement metrics in Q2. We continuously monitor and improve our filters and access, and expect them to improve over time.
In addition, while our product revenue initiatives are yielding expected results, they were slightly delayed primarily on Zoosk.
We have made good progress on delivering product enhancements in Q2. We deployed new aesthetics for Zoosk, and started testing them on EliteSingles and are seeing increases in user engagement. We introduced hCaptcha on all platforms to improve security, rolled out fraud and sales tax solutions and optimized pricing.
Our optimization work has led to an increase in average subscription length induced by 15%. This is good news overall, but we'll have a short-term estimated impact of reducing or reported revenues in H2, 2021 by $3 million to $4 million, which will be recognized in 2022.
We are starting to build social discovery features throughout our brands.
As a reminder, social discovery is people leveraging online activities, social media, and other communication platforms to forge new relationships and expand their social networks. We launched Zoosk Live!, a new live streaming feature on Zoosk iOS and Android app ahead of schedule in late Q2.
While still early initial user engagement in Zoosk Live! is encouraging.
We are particularly excited about the next date feature on Zoosk Live!, which allows Singles to speed date live streamers 24/7 through a 90 second video conversation on their phones.
We are working to further expand Zoosk Live! usage to deeper product configurations in the user experience and increased education and awareness campaigns.
In addition to increase user engagement, we also expect to see steady growth in monetization as users become more frequent visitors to describe. The company is in advanced discussions with an external partner to provide our users the ability to go on virtual base with other Singles. These new experience will initially be implemented on Zoosk under the name Zoosk [Great Date]. Zoosk Great Date will allow Zoosk paying subscribers to go on guided virtual dates to inspiring locations or events. Zoosk Great Date will include embedded video dating and chatting experiences for the daters, we expect to launch Zoosk Great Date towards the end of 2021. These new social features will have a positive impact on driving user engagement, and as a result, higher retention rates, more subscriptions, and increased ARPUs.
For work on Zoosk's product improvements and social features are critical in nurturing Zoosk back to growth. And while we have had a couple of delays in executing our roadmap, we are steadily turning the corner.
Additionally, we are pleased to announce we have signed an agreement with AARP to incorporate online dating tutorials and subscription offers for SilverSingles within the AARP ecosystem. This is the first step in expanding our reach in the over 50 demographic and educating them on the benefits of online dating. AARP is the largest organization catering to over 50 demographic, counting more than 30 million users and the two largest circulation publications in the U.S. A few words on COVID-19, we originally indicated that the listing of pandemic restrictions in getting back to normal life would have a neutral effect on our business.
We are more cautious today, given the uncertainty around the Delta variant and potential new lockdowns. We feel we are well underway on executing our plan to become the leader in social dating for meaningful relationships. But due to tighter security controls, a change in recognized revenue due to longer Zoosk subscription length delays in our product execution in a more uncertain COVID outlook, we have lowered our 2021 financial expectations.
We are on the right path to get back to growth and believe the current trajectory is a one and a half quarter delay versus our original plan, effectively getting the company back to growth in the first half of 2022.
For Zoosk, our target is to reach an inflection point by Q1, 2022 with the initial subscriptions showing year-on-year growth. Earlier this year, we communicated our intent to upgrade our core product functionality, expand our offerings to social discovery features and get back to organic growth.
We are making substantial progress on all fronts, and continues to be excited about the company's potential to strengthen its leadership position in the large and growing 40 plus online dating segment. I would now like to turn the call over to our new Chief Financial Officer David Clark. David, please go ahead.