In the announcement, Hawley's office emphasized the historic $2.7 billion in fines leveled by the European Union against Google for its anti-trust practices and a complaint filed by the Electronic Privacy Information Center with the Federal Trade Commission on Google's consumer tracking practices.
Federal regulators in the US also have investigated the company over antitrust claims, but Google settled with the Federal Trade Commission in 2013 without making any major concessions on how the company runs its internet search engine.
State Attorney General Josh Hawley said in a statement that he issued an investigative subpoena against the tech giant.
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Google didn't immediately respond to a request for comment.
In September, Yelp wrote a letter to the Federal Trade Commission that Google had violated a 2012 settlement by allegedly scraping photos from online reviews for its own search results.
Also of interest to Hawley's investigation is the roughly 70 percent of all card transaction information that Google collects.
Mr. Hawley said the state's preliminary investigation found that Google may be collecting more information from users than the company is telling consumers and that users don't have a "meaningful option" to opt out of Google's data collection.