Reviews won't move your book up Amazon's charts - only sales will do that - but reviews do sell books, especially if you're an unknown author. And Amazon is more likely to show your book to people searching for one in that genre/topic if you have 20-25 good reviews.
The only way to get book reviews is to ask. (Unless you want to buy them, in which case I recommend bookbub, as I've heard the most positive things about them.) For free reviews, start with people you know, then people in your FB groups, LI groups, etc., and move up to book reviewers.
Keep in mind:
1. Any review of 3 or more stars is a good review. Sure, it would be nice to have all 5-star reviews, but is that realistic? A 3-star review is fine. You might ask people if they don't think they can honestly give you 3 stars or better, to give you a brief critique, instead. This can help you improve your book without lowering your ratings.
2. Amazon likes reviewers who receive a free copy of a book for review, to indicate that they received a free copy. Don't be surprised or upset if a reviewer says that in their review.
3. Amazon puts a little "Verified Purchase" tag at the top of a review of a book that was purchased by the reviewer on Amazon. Fair or not, reviews with these tags are more valuable than reviews without.
Where do you find book reviewers?
Check out sites like Choosey Bookworm, Book Pleasures, and Readers Favourite.
Check Amazon's lists of frequent reviewers. Click on http://www.amazon.com/review/top-reviewers for their top reviewers. Click on a name, and you'll see all their reviews plus the reviewer's e-mail address in the lower left corner of the page. Make sure they review books in your genre before sending them a personal email request to review your book.
You can also use keywords on Amazon.com to find books like yours and see who reviewed them.