Claire Ballentine

Online advertising companies have struggled for several years as Google and Facebook solidified their grip on digital dollars, slowing revenue for the others. Now, many ad tech companies and their investors are throwing up their hands. Venture capital money going into ad tech start-ups is falling sharply, helping push a wave of consolidation. Financing reached a high of $2.92 billion in 2015, but this year, it is on pace to be less than half that, according to CB Insights, a financial research firm.