You can’t "sponsor" a tourist visa in the same way you sponsor an immigrant, but you can help support their application.

You can write a letter of invitation explaining why you want your friend or relative to visit the U.S. and how long they will stay and in the invitation letter, you can promise to provide housing, transportation, or financial support during their visit.

You can submit an Affidavit of Support (Form I-134) if you want to show you will financially support their trip.

You can submit an Affidavit of Support (Form I-134) if you want to show you will financially support their trip.