how to grow a new social network

We build a social network.. We're not the expert on the market stuffs but actually it's as hard as developing a new stuff.. Anyway I'm just curious about how to grow a new social network..
I know it's all about make a meaning for people and help to solve a problem for users..
I think we have validated it because most of users are coming back.. Also we always implement new features to increase engament for existing users..
Actually what we try to do is "Lean Startup" ..

But It's really hard to get new users.. It's not because they dont want it, it's because actually they dont know that there's a network like ours..
So how can we aware people outside about what we have done?

We decided to implement basic stuff like invite friend from other networks (facebook,gmail,hotmail and etc. )

Then also we'll implement a social connect to post to existing networks(facebook,twitter) for behalf of our users.. A little bit spamming in people news feed.. let say each of our users has 200 friends.. 10% of them see posts come from our app and %5 of them register, I think it's pretty much good signals for a very early stage network..

I'm really open to any suggestion and excited hear from you..
Thank you,

I think you should start by entering or cooperating with some specific communities, such as school, mid-sized business communities, sports organization, and etc. Then facilitate those communities with your unique features, so that they become an active and solid networks in your social networks. If you have succeeded with one community, then go with another. By the time, your social networks will get bigger and bigger.

@tylerdurden I give a practical example what I am doing right now. I recently started a site for the students in India. Now what i want is to increase my visitors and involve them in activities posted on my site.
I did following for the same :-

1. Created a small team for promoting us on social networks like FB.
2. Offering perks to team members so that they work well. I am also planning for organizing some contest kind of thing so that we can get more subscription.

So what you can do is:-

1. Create a team from different region to promote yourself.
2. Dont spoil your content as it will give you the returning users.
3. Keep upgrading things on social networks.
4. Organize some contest so that users gets involved.

You can do it. Wish you all the best.