Social media bounties have the least promotional effect, but generate the most amount of spam. You said it yourself, if you have a Facebook account with thousands of friends and followers from all spheres of life, what are the chances they have any interest in crypto and are going to like the content you share? Instead of generating an interest in the project, you end up with nothing. Those posts and comments have no likes, shares, comments... No one wants to see them. And you will be limiting your friend circle who will eventually get sick of your posts and block you.
I admire those who create many alt accounts to participate in bounty.
You shouldn't. That's how you get negatively tagged or banned if one of your alt gets banned for any reason.