The girl is said to have changed her appearance to look exactly like the singer's partner Eleanor Calder, reports The Sun.
Fans at the show in Houston, Texas, started coming up to her after they thought she was actually Calder. Security then took the girl inside the venue, assuming she was waiting for Tomlinson.
"Fans outside the gig believed this girl was Eleanor and started hounding her about Louis and asking for her autograph," a source said.
"Security saw the commotion and took her inside the venue to present to Louis, who obviously told them it wasn't her."
Tomlinson was recently startled to find a naked man trying to get into his hotel room in Stockholm.
He has been dating model Calder since September last year, and recently described her as "down to earth".
Watch One Direction's video for 'One Thing' below: