Yes, almost certainly.
There is ample documentation that many of the workers in cocoa factories in Cote D'Ivoire are trafficked, which essentially means forced to labour against their will. Wikipedia has the basic facts:
In 2002, Côte d'Ivoire had 12,000 children with no relatives nearby, which suggested they were trafficked, likely from neighboring Mali, Burkina Faso and Togo. According to a 2009 snowball sampling study, the majority of those with childhood cocoa labor experience were trafficked (75% from Burkina Faso and 63% from Mali). The majority of those who were trafficked had no interaction with police, and 0.5 percent had any contact from institutions that provided social services
In 1998, UNICEF reported that Ivorian farmers used enslaved children—many from surrounding countries. A 2000 BBC documentary described child slavery on commercial cocoa farms in Côte d'Ivoire. In 2001, the US State Department estimated there were 15,000 child slaves in cocoa, cotton, and coffee farms in Côte d'Ivoire, and the Chocolate Manufacturers Association acknowledged that child slavery is used in the cocoa harvest.
Wikipedia provides references to support those statements.
As for whether the chocolate you buy is produced by these slaves, The University of British Columbia Project Terry writes:
Child labour and child slavery is a prevalent issue in Cote D’Ivoire, the top cocoa producing country in the world. 40% of all cocoa beans come from Cote D’Ivoire, which makes it almost unavoidable for companies such as Mars, Nestle, and Hershey’s to avoid having these beans in their products.
The Confectionary Industry's own newsletters acknowledge the problem. The BBC has repeated stories. New organizations from the UK and Canada have picked up the stories. The US Department of Labor considers it an issue.
In short there is an abundance of evidence for this.