Since the social networking giant went public on May 18, with a share priced at $38.
However shares fell by 11% on May 21 and a further 9% on May 22. The shares are now worth $31 each.
As the share price continued to fall, regulators said they may review the disclosure process to see if some investors got favourable access.
The Securities and Exchange Commission and regulatory body Financial Industry Regulatory Authority both said they would look into the matter.
The IPO of the social networking giant was named as the third largest in the US history but, analysts have said that it has failed to live upto the hype initially created.