Boost facebook post in groups

Hi guys,
a small question.
How is it possible in a huge private group to boost someone's post with the same hashtag of many others, without sponsoring it?
I saw many differences between two similar posts, with same hashtags. It is not a matter of being old/new member, editor or admin. Is there really an algorythm or an option to select for group admins?

Thanks!

no idea?