If I hear about a market that might suit one friend, I let them know. They do the same for me. We watch out for each other. Again, if one approaches making friends with the idea of they can be useful , then nothing will ever come of such a relationship. I have known one person to choose and discard people on the basis of whether they were useful for her career or not.
Friends are most important.
They cannot be bought or bartered. I have made friends a long time ago and many years down the track I have either been of assistance to them, or they to me, in ways neither of us could have foreseen. I ll let you decide. But the greatest tool a writer has for publicity and self-promotion is the tool at their fingertips. If they are on-line, so much the better.