Short answer is everyone is on Facebook (or at least knows several people who use Facebook) and you can target individuals more specifically than you can with Google.
For example, if you are a company that sells anything to do with weddings be it flowers, dresses, cakes, invitations etc. and your business is located in Waterford, Ireland, you can target all the females within 50 miles of Waterford, who are engaged or in a relationship and get them to join your company facebook page.
If you are selling GAA merchandise you could target all the people from a certain towns and who have an interest in GAA.
In fact most businesses can get access to their target market very easily through a few simple clicks. What’s more Facebook approximates how many people you will potentially advertise to based on your criteria selection. You can also target by gender, age and interests etc., you can even target by work place (if users have that set, unfortunately most users don’t set that field).
You can also get a bit more advanced with it and only advertise to friends of people who are currently subscribed to your page, or exclude people who are in certain groups or pages already.
The beauty of it is that once you have someone on your page you can repeat advertise to them for free and what’s more their friends will see your messages via page updates on their profile. This is the beauty of Facebook advertising i.e. your money doesn’t stop working for you once the user clicks like on your ad.
Google ads has it’s own advantages, generally when people search online they search in surf mode, comparison mode and buy mode through the use of keywords and phrases. You can get people coming to your site looking to purchase your goods if you get the key phrases right and not only will your ads appear on Google’s search results page it will also appear on other webmasters sites whose page topic matches the advert in terms of keywords and phrases.
The problem with Google is that you cannot focus in as specifically as with faceboook and you only get 1 shot at selling something based on the money you spend on a click.
So depending on your business Facebook could be an ideal way to capture your market and you can grow from there.