It's common. A friend of mine was posting two or three anti-Trump/anti-Republican posts per day on my Facebook feed. He then came out and said in one of them that he was proud to volunteer for a group of Internet activists on behalf of the Democratic party. He kept doing it, and I had to 'unfriend' him eventually. There are groups of these people in most metro areas, and they work together to share articles, review talking points, etc. to push their narrative out. I don't know if they're compensated or if they just volunteer.
Obama started this as a formal program. It was connected with his "American youth corps" idea. The program, as a whole, sounded eerily similar to China's Red Guard, which started during China's cultural revolution. It didn't gain much traction though.