A personal hashtag can help make the brand look more authentic and a good way to make people use ones hashtag is by promising them features on your account if they do so.
What are other ways to make them use your hashtag or either tag you in their posts?
Feature their post and then ask them to tag you in their original post, and for more features in the future. If they don’t use it, delete the post and move on.
Then DM other people and do the same, eventually people will start noticing the hashtag and do the same in the hopes of a reposted feature, if your account is big enough.
Really there has to be a reason for people to want your attention, if you offer nothing to them (small audience, bad content, etc) then nobody will use it / tag you.
You can have a “post of the day” or a “post of the week” story feature. Every day/week you can choose one post that has your hashtag and feature it in your story. The second story after this will be an instruction slide “use hashtag to get featured blah blah”. Might give more visibility to these people and might get them to start using your hashtag.