I posted in "who wants to be hired" a few times, and a few people reached out. About 50% seem to be somewhat targeted to the message. At least one lead to an offer (which I declined for other reasons, it was a fair and interesting offer though).

"Who is hiring" never worked out for me, as the geographic limitations are too strict or confusingly worded. Looking through 400 posts to figure out which are actually open to hire someone from europe is not as promising as looking through dedicated job portals.