Digital advertising is still in its Wild West days. The market is in a state of continual flux, and purchasing banner or "display" ads on websites gets increasingly complicated by the month, as automated auction sites send banners flying around the Internet.

By the nature of the beast, there's no central directory where marketers can look up who's running ads where. A bit of intelligence is a valuable thing.

The young founders of WhatRunsWhere discovered this by accident. The company's CEO and COO, Mike Cojanu and Max Teitelbaum, were both running their own digital advertising businesses – Mr. Teitelbaum since he was 15 – when Mr. Cojanu set about building a tool for his own internal use. As he devised marketing campaigns for his clients, he thought, wouldn't it be useful to get a picture of what other advertisers are up to?

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So he built a tool that, if it couldn't give an absolute answer, it would give him a reasonable picture. He programmed software bots to "spider" the Internet much like Google does: automatically surfing pages the way a human would, taking down notes about the ads it encounters, and building a data base of what's going on.

The result was a tool that, Mr. Cojanu discovered, advertising clients were very interested in. Mr. Cojanu and Mr. Teitelbaum – already acquaintances as young men working in the same circles – joined forces and WhatRunsWhere was born.

The firm chiefly targets four markets.

WhatRunsWhere's latest offering tracks an even trickier query: Ads that are served not on the open web, but inside Android applications.

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"Big Data's such a buzzword, but we're a large data company," says Mr. Teitelbaum who, at 22, manages the firm's sales, marketing and operations from its Toronto office, while 24-year-old Mr. Cojanu runs the engineering side from San Diego. (The pair co-ordinate with three formal video chats a day, in the morning, noon and evening.) Demand has been steady enough that Mr. Teitelbaum says the firm never had to raise money – it's been profitable from the start. Today, it's grown to a staff of 15.

It's not the only company to do ad tracking, with behemoths such as ComScore and Neilsen already in the space. But Mr. Teitelbaum says WhatRunsWhere's service is more complement than competitor. For one thing it's relatively cheap, starting at a subscription of $229 per user. For another, its coverage is widespread, across 15 countries, and frequently updated. Since nobody can claim to know what's out there with 100-per-cent certainty, every data point helps.

Given that uncertainty, how do customers know the company's data is good? Mr. Teitelbaum points to one easy test: He says customers report that the results they find while searching for the ads they themselves are running – the one data point they know for sure – lines up with reality.

"We don't claim that we capture every single ad that runs online, but we do give a very good picture of what's happening in the online landscape."