Regarding magazines, I rarely use platforms like Kavyar. Sometimes, yes, but I usually prefer personal contact with the editors (when they reply… :D). So I do much research to find current contact information and reach out personally. However, I use Kavyar as another platform to showcase my work and this way, sometimes, magazines reach out to me…
It’s the same with agencies and art buyers, as there are many platforms out there trying to ease this step, but the personal contact gets lost through that (and it probably results in lower fees for the creatives).
In my experience, most often, personal contact to agencies seems to be most promising but you have to be lucky as well – because if the timing of your contact is right they are just about to start a project for which they are really looking for creatives.
On the other hand, many times, there’s just not the right project in the pipeline… Then, there’s no way around trying again later, considering that next time there might be a different contact person who needs to be convinced again or other obstacles 🙂