Google's search market share has seen a decline each year from 88 percent in 2011 to 78 percent in 2016, Forrester says. Although Google's search ad biz grew at a solid low-teens rate over that period, the market as a whole grew faster, Forrester says, with mobile spawning more competition for Google. Forrester says Amazon is exploiting Google's "weakness" in online shopping, as shoppers are increasingly starting their product searches on Amazon instead of Google. According to the report, consumers are 2.5 times more likely to find out about the brand of a recent purchase from Amazon versus any other search. "This erosion is likely to continue" for Google, the report said. Forrester adds that CPG (Consumer packaged goods) marketers are also likely to greatly increase their ad spend on platforms like Amazon, which has its own search ad business. Get the full story at AdAge