I would like to highlight 2 ways I am using to promote this site, and get friends on it. Many people are unaware and we need to show the usefulness of this site.
I am using a stackapp - stacktack which is a small widget that we can place on other sites where it is possible to like blogs.
You can see it in action on my site page, where I am displaying few of the hand-chosen post. All you need to do is include few lines of code, and give the question id which you see in the url. If anyone is not from a programming background, I can help you out with this. We can start a chat on this if required.
On any main question page of islam.se, on the right side you can see the following link to subscribe for a weekly newsletter.
This gives a summary of popular, quality, high voted questions and answer. I forward this mail to my other friends. This is a quite a good way to let people know, what all kinds of discussion is possible and also they get to know the proper authentic answers with references.
Hope, you also start using above ways to promote the site. This will be effective. Feedback is welcome.