I am currently writing a book to be launched on kindle Amazon. My list is made up of fans but not potential buyers.
If you are looking for a free method then try the following -
Create a contest. Email your list of 100 fans and tell them they will get the following -
Their name in a special acknowledgments page in the book and a 50% off coupon for the price of the book if they share the link to your Amazon book page with one of their social networks.
Set a date for the contest to end maybe 2 weeks out. Whoever has the most shares across all of their social networks in that time frame (FB, Twitter, Instagram, LinkedIn, Blog, etc) will win a character cameo with their name in the book and a free copy of the book.
This would require writing in an ancillary character into a scene in the book that has no significance to the story but is just a way to mention the contest winner's name.
For each share, the contestants just need to email you the share link to prove they made the share.
