Hi I am the owner of http://www.forumportables.fr, a localized forum (in french) dedicated to mobile phone and computing convergence. I am earching for a way to attract visitors , difficult to get some posters. Thanks for help
Well one advantage that you have is that there probably aren't many similar sites in French so competition won't be as bad as if it were in English. I see you have some basic SEO implemented already which is good, might want to analyze your traffic a bit better with Google Analytics to see what keywords are working for you and consider buying some ads on some French sites to drive some traffic. You could also post on other French forums and add your link in your signature to spread the word for free, but make sure they allow that and that you're NOT spamming their website, just contribute useful things.
find blogs and forums related to yours get some nice traffic that way and if they are do follow you get backlinks which help you rank higher in serps and have more targeted traffic also try contest thats what i'm doing on myforum works pretty nice. Just takes a lot of time.