CB Insights, the venture capital data specialists, also revealed there was a 33% fall in the volume of funding over the past year, from $3.2bn to an estimated $2.2bn.
And looking at the figures on a quarterly basis, just 69 adtech deals were completed in Q4 2016 to date, the lowest level of activity in any quarter since 2012.
These are some of the headline findings CB Insights produced for the Financial Times, which reported that ad tech start-ups are struggling to attract investment as Google and Facebook become increasingly dominant in the digital advertising sector.
The numbers bear out the explosive growth of Google and Facebook's share of the ad market, the Financial Times reported, as it pointed to research published last June that found the two social media giants accounted for 75% of all new online adspend.
"Adtech's struggle as a sector is absolutely to do with the dominance of Facebook and Google," said Suranga Chandratillake, a partner at Balderton Capital, a venture capital firm based in London.
"Ultimately advertising is about selling attention, and if most of that attention is focused on Google and Facebook, then naturally they can monetise it," he added.
Chandratillake went on to explain that the problem for many adtech start-ups centres on how to build the same level of scale that Google and Facebook can command.
"Gains in adtech are increasingly marginal because companies are constantly copying each other. Lots of adtech start-ups go from zero to $30m of revenue and back down to zero again. As a VC that's hard to back," he said.
"Even if you manage to build a sustainable advantage for a few years, how do you scale to compete with Google or Facebook? That's why traditional adtech does feel dead from a venture perspective."
Data sourced from Financial Times; additional content by Warc staff