How can I encourage more members to join a website for webmasters, and freelancers? It's hard.

Yep, it is hard. But, like any member based website there is no big secret involved. It requires the following:

hard work
providing something people really want
giving it to them in a way they like
giving them a reason to keep coming back
more hard work

Alright, thanks for the advice!

Good luck! Unfortunately, that's a really oversaturated market right now (there are way too many webmaster forums out there). You might wish to provide free classifieds ads for the freelancers.

Free ad sites
Pay Per Click
Spreading the word (forums, blogs)

.. A lot of work!

You need to offer something of value. Ask your self what can I offer that the other site's don't have..

Also try to build incoming traffic. You can have the best site in the world, but if you dont have a traffic and marketing plan, you will sit their and waiting for traffic..

Setup a blog and submit blog directories, the same for articles and submit to article blog directories. Their are many other ways to get traffic, do a search on this forum ..

Like cscgal has said, their are many forums online with your topic, I thinkg what you should do is sub niche niches topics..

But I would advise build traffic first..