"They may or may not have legal immigration status. Victims may be fearful and unable to speak freely, so it is best not to make assumptions about what you see. For example, don't assume that because a person has a cell phone he or she is 'free to leave.' Don't assume that all individuals charged with prostitution are participating in the sex trade voluntarily. Instead, when handling these cases, recognize that defendants may actually be human trafficking victims. Under federal law, any person under the age of 18 induced to engage in commercial sex is always considered a human trafficking victim, regardless of force, fraud, or coercion."
Department of Homeland Security: https://www.dhs.gov/