State Attorney General Josh Hawley said in a statement that he issued an investigative subpoena against the tech giant.
The investigation will focus on Google's use of data, as well as allegations that it discriminates against competitors in the search results.
He says the company will be held accountable and Missouri is not giving Google a free pass.
Hawley's probe intends to look at how Google collects information, and how and what they share about somebody's online activities. He says "substantial evidence" suggests the company might manipulate search results to list Google-affiliated websites higher in search results.
In June, the European Union issued Google a record $2.7 billion antitrust fine.
"We have not yet received the subpoena, however, we have strong privacy protections in place for our users and continue to operate in a highly competitive and dynamic environment".
Hawley's office argues that federal regulators were wrong not to sue Google and that inaction left an opening for a potential state suit.
"There is strong reason to believe that Google has not been acting with the best interest of Missourians in mind", said Hawley, a Republican running for a US Senate seat in 2018.
Hawley on Monday said he also agrees with sentiments from the White House, saying Moore has a right to defend himself against the claims reported by the Washington Post. The attorneys general of Utah and the District raised a flag past year, urging the Federal Trade Commission to reopen its investigation into Google's search practices, although the agency has not said it would do so.