This is a small sample of websites that might be useful for your research:
Trafficking in Persons Report / U.S. State Department (see link to 2013 report and others on left side of screen)
Office to Monitor and Combat Trafficking in Persons / U.S. State Department
Human Trafficking / United Nations Office on Drugs and Crime (see additional links on left side of linked page)
Global Report On Trafficking In Persons / United Nations Office on Drugs and Crime
Forced labour / International Labour Organization
Palermo Protocols (United Nations Convention Against Transnational Organized Crime and the Protocols Thereto / United Nations Office on Drugs and Crime) (see p. 41 for protocol related to trafficking)