Make your ARG more realistic:

• Refer/embed [to] real places
• Refer/talk about [to] real activities
• Start a website they can access freely
• Start a website that requires a key/clue to access it
• Get a good artist to design your logo and webpages
• Suggest a website where they can discuss the ARG privately
• Set-up dropboxes/places all over the country that you are in
• Set-up a post office/UPS box
• If they give you real addresses send mail/express mail them with clues
• Advertise for “players” in craigslist, twitter, etc.

There are some tools you can use to make the ARG more real, for instance make a recording (youtube) of a person extolling the virtues of your product, etc.