New York Attorney General Letitia James said the investigation now has the support of 47 attorneys general from around the nation, "who are all concerned that Facebook may have put consumer data at risk, reduced the quality of consumers' choices, and increased the price of advertising".
"We will use every investigative tool at our disposal to determine whether Facebook's actions stifled competition and put users at risk," James said in a statement late Tuesday.
The investigation launched last month with support from attorneys general from eight states New York, Florida, Colorado, Iowa, Nebraska, North Carolina, Ohio, Tennessee and Washington, DC.
Facebook had earlier said it will work "constructively" with the attorneys general and engage with policy makers in a discussion about the competitive environment.
"Social media is a critical part of doing business in today's economy. Any effort by Facebook to unlawfully stifle competition could cause wide-ranging harm to smaller companies, restrict consumer choice, and increase costs for all," said Connecticut Attorney General William Tong.
According to Delaware Attorney General Kathy Jennings, "We are investigating whether Facebook has broken the law through anti-competitive practices or other acts that harm consumers."
In a stern warning to tech giants, the US House Anti-Trust Committee has opened probes into Facebook, Google, Apple, Amazon and other tech giants to determine if they prevent competition and hurt consumers.
The investigation's core is the idea that "the Internet is broken".
"Big Tech must account for its actions. I am proud to join my Republican and Democrat colleagues in efforts to ensure Tech Giants can no longer hide behind complexity and complicity," said Louisiana Attorney General Jeff Landry.
Massachusetts Attorney General Maura Healey added: "It's important that the internet remains fair and open to everyone. We are participating with a broad coalition of states in an investigation of Facebook's business practices."
A bipartisan coalition led by New York attorney general has launched an investigation into Facebook to understand whether it stifled competition and put users at risk.
"The District of Columbia has joined this investigation to ensure Facebook is giving a fair shake to district residents and the American people. No company gets a pass if it throttles competitors and exploits consumers," said District of Columbia Attorney General Karl A. Racine.
( With inputs from IANS )