Hello @Tran3,
Having someone new as a co-host won't affect the visibility of the listing in searches.
He won't be able to gain superhost status as a result of his co-host activities for you.
Superhost status is granted only for activities when hosting one's own listing.
His co-host activities can affect your ratings and superhost status as all reviews and ratings that guests leave as a result of their stay will be on your listing and profile, not his. It would be a good idea to go through with him all the categories in which you can be rated and agree the way that each should be approached.
The articles below have information on what can affect the position of your listing in search results and what co-hosts can & can't do.
Your-top-questions-about-Airbnb-Search
What can a co-host do?
Steve.