My .02, forget about the number of fans you have and concentrate entirely on the level of engagement you have from your existing fans.
Some ways to do this are:
Upload a picture of a very hot car you have on the lot, nothing else, just the image. You are sure to get some replies to it. After a couple people reply, get into the conversation.
1. What did they say about the car?
2. Was there a particular feature about the car they liked?
3. Did any of them own this type of car before?
If you don't get any replies, keep trying other images until you do.
Find communities made up of community managers and beg for advice:
Online Community Managers | Facebook
This is hard work, extremely time consuming, but also priceless if you get a true following.
Once you've mastered this, do the same with your blog and write articles you think your community will comment on. Then ask certain members of your community to become moderators or admins. If you are building a real community, a destination on either a fan page or a blog, you'll need help once you get traction.
When you feel you've got some good results from pieces of content you've shared, you can crank it up a bit. Instead of one image every week, try getting one up every day, and ones people are commenting on. Then get your users to submit their own to you, ask them to send in pics of their first car or whatever they seem to be interested in.
Keep the conversation going, ask them questions, answer back as if you're always there on the page. They'll start coming back if you're adding a lot of content, and then fine tune it. Start adding your content at the same time every day so they get into a habit.
There's lots you can do, just depends on what you want it to become.
