By coincidence, I was just writing a post about Twitter. If you use Twitter, you can tag tweets (or posts on Google+) about memory with the hashtag, #mnem, and other users will be able to reply to them. (Any language)
Maybe of these pages would help with finding French users:
http://freenuts.com/search-twitter-users-by-location/
http://wefollow.com/twitter/french
http://wefollow.com/twitter/france