This book was converted from its physical edition to the digital format by a community of volunteers. You may find it for free on the web. Purchase of the Kindle edition includes wireless delivery.
Albeit slightly repetitive because it's a compilation of essays from clergy, missionaries, victims, and law enforcement, this book published by the Midnight Mission of Chicago contains a variety of statistics and common beliefs from the era. You may want to view these with skepticism as this is a piece of propaganda written to "wake up" concerned parents and citizens but the research appears thorough, often culled from crime reports, health authorities, victim's testimonies, etc.
That being said, trafficking has not changed much over the past hundred years. Most of the ploys have remained the same for both foreign and domestic prostitutes, the only difference being the suppliers. I'd like to think American girls are more savvy these days, but then I remember how many runaways become streetwalkers due to the exact same schemes.
Great book to start examining the modern American backlash against legalized prostitution via the brothel system and/or segregation to "red light" districts. Also interesting from a gender studies perspective to examine the tension between more freedom for women and fears of less supervision.