Google found that Russian-linked entities bought tens of thousands of dollars worth of politically motivated ads on its platform around the U.S. presidential election, according to people familiar with the investigation, the first sign that Russia’s alleged attempts to influence the 2016 vote spread to the world’s largest advertising business.

Similar to ads that ran on Facebook Inc., the ads on Google touched on a variety of hot-button social topics, without a clear bent toward one candidate or political position, these...