If you need to facilitate an interactive training session and you do not know all participants, you may want to ask your audience to create a simple name tag. This can be done by having a simple sheet of paper fold in two and let the participant write her/his name on each side of the paper and place this in front of them.
You can use this during your training / presentation to call out and ask question to individual participants by mentioning their name. By means of this you create a much more interactive session and the audience will get the impression that you know them. Simple and easy.
Look for more tips about creating an interactive presentation in the book that is part of the Public Speaking Kit.