Search for a successful tell-a-friend campaign?

I’m looking for a tried and tested tell-a-friend campaign. Who has got a successful method for me to copy?

We are running a small company in The Netherlands, selling design furniture to consumers, mostly via internet and also in our store in Den Haag.
In order to reach critical mass our objective is to multiply or triple our existing customer base. We think to do that by running a simple tell-a-friend campaign via e-mail.