CathInfo.com

For starters, don’t flirt. Girls who flirt look like airheads.  Boys who flirt look like 🌈.
Just be yourself.  See a girl who interests you?  (Other than just looks!)  Go introduce yourself and tell her what attracted you, like her interest in books, how she treats others, her friendliness, sense of humor, etc.  Be natural and sincere.
Maybe sit down and have coffee across from her after mass.  “Do you mind if I sit here?”  How does she reply?   If positively, make a little small talk by asking questions about her.  Where does she live?  How many siblings?  What about her school or job?  Any special goals, hobbies?  Unless she asks back, say very little about yourself.  Keep the introduction short, 10 minutes, tops, in the presence of others.  End by “needing to go now” even if you don’t.  Go talk to your parents, or go to the car.  Don’t just run off, however.  Say, “Nice to meet you.” Shake her hand if it’s customary.  “Hope to see you next Sunday.”  (Or next month, next Mass…)  If she’s just visiting or passing through, and you REALLY like her, it’s probably okay to request her email.  
Another suggestion is attend one of the young people’s gatherings. There are at least two listed here on CI in the last month.  You might also try online.  Personally, I’d never even consider that, but I’m old.

In my Church there are very few single girls.

Where should I search?

Then I would start right where you are.
What communications do you have with these young single woman? Have you made approaches to any of them?