Want to Get Noticed by a Celebrity? Snag Their Username on Social Media

In 2018, then middle-schooler Adrianna Wagner became smitten with professional baseball player Christian Yelich, after the Miami Marlins traded the left-fielder to her home team, the Milwaukee Brewers.

The teen, who lives in Alma Center, Wis., started a TikTok account to post fan videos, using Mr. Yelich’s name as a handle. She figured people searching his name on the app might come across her account and give it a follow.