Formal:
* Y a-t-il des Français parmi vous ? (Is there anyone French among you?)
* Est-ce que quelqu'un ici est Français ? (Is anyone here French?)
Informal:
* Y a des Français ici ? (Are there any French people here?)
* Quelqu'un est français ici ? (Is anyone French here?)
Direct:
* Qui est français ici ? (Who is French here?)
The best option depends on the situation. For example, if you're in a formal setting, you should use a more formal phrase. If you're talking to friends, you can use a more informal phrase.
You can also use the phrase "parlez-vous français?" (do you speak French?) if you're looking for someone who can speak French.