Digital 100 Winner Carla Car Rental’s Recipe for App Growth

Carla Car Rental Cofounder Izi Aviyente on building a mobile-first travel agency that was just recognized in Digital 100 as one of the fastest growing travel apps in the US.

For Carla Car Rental cofounder Izi Aviyente, winning a Digital 100 award was a pleasant surprise and a “validation that we’re on the right path. SimilarWeb is a product we’ve been using for the past couple of years, and we’ve definitely found it to be really trustworthy. We look at a lot of the competitors’ data in terms of where their traffic is coming from, and getting that validation from a brand like Similarweb was definitely a big milestone for the team,” he said.

The Digital 100 is Similarweb’s annual ranking of the fastest growing websites and apps. Although Carla is a Similarweb customer, that’s not a requirement, and this is not an award companies apply for or lobby for – it’s given to companies that demonstrate the best performance, according to Similarweb estimates.

Carla’s mobile app placed #3 in the Travel & Tourism category of the Digital 100 ranking for the US, having increased monthly active users by 74.8% for the 12 months ended November 2025, versus the previous year. In comparison, the #1 app from rental car company SIXT increased MAUs by 225.9% – but the two are not direct competitors. Carla is an online travel agency that helps consumers find and book the best rental car deals, including cars from SIXT.

Founded in 2016, Carla had one of its strongest years for growth in 2025, powered by a global expansion of its marketing and the maturation of its data and systems. The rentcarla.com website saw a traffic increase of about 125% year-over-year, or more than some Digital 100 website winners, but didn’t meet the minimum traffic requirement to be included in the travel website ranking. Carla has a strong mobile-first strategy, accepting reservations on its website but strongly encouraging customers to download its app.

We interviewed Aviyente at the end of January, shortly after the Digital 100 awards were announced.

The full interview

As mentioned in the video, Carla didn’t necessarily show increases every month of the year – Aviyente said they chose not to spend as much on advertising when ad rates were high in November and December, leading to traffic and app usage dips for those months – but the overall trend was strongly positive.

Finding inspiration in HotelTonight

One source of inspiration for Carla’s approach when it first got started was HotelTonight, which Airbnb acquired in 2017 and continues to run as a semi-independent booking agency. Originally a specialist in same-day bookings (thus the name), HotelTonight designed its service to present customers with a shorter list of recommended choices, rather than overwhelming them with hundreds of possibilities. Carla set out to do something similar with rental cars, rather than hotel rooms.

If you research rental cars on other online travel agencies, you will see “many listings for the same car, with a $1 difference,” Aviyente said. Carla deduplicates and personalizes that list, he said. “We show you fewer options, but ones that are more likely to convert.” At first, delivering that targeted list was hard because Carla was still working on the basics of getting the right data. But after 10 years, Carla has amassed the quality data needed to do AI-powered analysis and personalization of offers, he said.

“If we don’t know the traveler, then we can fall back to geo-popularity – which is going by what’s popular in that area. But if you’ve booked with us in the past and we know you prefer SUVs over economy cars, or you prefer intermediates, we can personalize based on that,” Aviyente said.

He also wants to improve Carla’s brand visibility in GenAI platforms. Carla has a Custom GPT customers can use to research car rentals and is actively working on integrating the full booking and payment experience into ChatGPT and other AI models, he said.

Meanwhile, Carla is looking to expand internationally. In 2025, that primarily meant advertising to travelers inbound to the U.S. from the UK, Europe, and other markets. “Technically, they could have been doing that for years, but we hadn’t put marketing dollars into capturing those segments.” In 2026, Carla will also increase its focus on outbound travel from the U.S. to other countries, he said.

Some of Carla’s advertising drives traffic to its website, although in other cases it drives people straight to the app stores. “We’ve definitely seen that in some markets, driving them to the website has worked well for the sort of initial launch, but we definitely push the experience to mobile, where possible,” Aviyente said. “Even if they convert on the website, we definitely encourage them to download the app.”

How the Carla mobile website promotes downloads of the mobile app.

How the app promotes deeper customer relationships

Carla emphasizes getting its app on customer phones because that makes it easier to do follow up, which can be important to ensuring a good customer experience – a big priority, Aviyente said.

“The average NPS (Net Promoter Score) for car rental is minus 1,” Aviyente said, referring to a standard measure of customer satisfaction. “A lot of things can go wrong along the way.” 

While Carla has API connections to the systems of its suppliers, the inventory of cars is always a projection that can be thrown off by customers failing to return cars on time for other customers to be able to rent them. Carla may not be at fault for all the issues customers encounter with their rental, but it still needs to accept responsibility as the company that booked the rental, Aviyente said.

Through the app, Carla aims to deliver more guidance to customers, for example by alerting them in advance to a problem with their booking and trying to help them make other arrangements. The app also reminds customers about the documentation they will need to provide, Aviyente said. “We have customers trying to present a digital version of their drivers license, and it would be great if that worked, but the car rental companies are still expecting a physical drivers license and physical credit card.”

Carla also works to promote visibility into car rental company terms and conditions, as well as surcharges like additional fees for young drivers, he said.

Just as important as the outbound marketing is the nurturing of customer relationships through Carla’s Customer Relationship Management system, including follow up emails and push notifications through its app. “I’ve worked in other marketplaces before, and the challenge is not to get the customer from zero to one – it’s mostly getting them from one to two,” Aviyente said. “Once you get to two, getting from two to three or four trips is much easier.”

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by David F. Carr

David covers social media, digital advertising, and generative AI. With a background in web trends since the 1990s, he’s also the author of "Social Collaboration for Dummies".