I think that participating in the discussions and asking questions is a good beginning.  It is sometimes difficult to find a language partner, especially in English, simply because of supply and demand issues.  You could also chose to work with a tutor or a teacher as well.

Here is a link to help you get started on italki: http://support.italki.com/forums/20939611-Language-Exchange

As a native English speaker, I get 20 or so messages a day. I only help those people who are native speakers of my target languages, so I would first suggest that you contact only those people who are learning one of your native languages. And then, it is best to try and make it personal. Don't just write "help me learn English". Try using their name and commenting on how you noticed they are learning your native languages, and offer to help them in exchange for their help. For example "Hello Sarah! My name is Shahin and I noticed that you are studying my language. I was wondering if you might need some  help, in exchange for helping me with my English?".

You might try correcting some journal entries in your native language(s) too, as this will make you more visible. If not, as Becky has suggested, you might try working with a tutor. 

I added you on skype