First off i'd like to point out that .tk isn't a paid domain, and a lot of people know that. You'd be better off with a .com, .net, .org, ect. I'm not going to say this is seriously hurting your traffic / activity, but with virus scares and such these days people are less likely to click on a link with an ending that sounds foreign.
Your skin was a nice choice, it matches your theme perfectly. However, most other Apple / Mac forums also use that skin, so yours is nothing different. I'd suggest editing it some, making it more custom to your forum (not sure if you can do this on the free host, however, which brings me to my third point).
Free hosts are turn aways. I don't join many free forums, and I know many other people don't as well. I'd suggest getting your database and moving to a paid / free web host, installing a real copy of phpBB, and learning the system.
If you really would like your forum to succeed, i'd start with those suggestions 🙂
I believe your skin has nothing to do with your traffic As it's a very appealing skin for your kind of website your trying to run. I think you should hold some contests maybe giving away iTunes cards ect.. Basically to run a successful website you have to have what your competitors have yet even more, Offer things that others don't.
While the looks of the forum matters, that's not always why it isn't attracting new members. You need to advertise your forum in signatures on other forums that you frequently visit, as well as telling people you know about it, so word can be spread quicker.
Sometimes, it can takes months and even years to create a successful forum. It's all about patience. A trick that I've learned is to create multiple accounts yourself, and have fake conversations, so that if a visitor sees the forum, they won't think it's dead and will probably join. Another way is to make your forum more interesting by adding videos, pictures, games, etc.
