1. Are you who I think you are?!
  2. It's you!
  3. Girrrlllll!!!
    Alternatively: Boyyyy!!!!
  4. Oh! You! Stop right there! How are you?!
  5. It's been so long, friend!
  6. You! Over there! My friend!
  7. Hey What's-Your-Face!?
    Suggested by @BrentMWiggins
  8. Pretend to be British, ideally an old British lady
    You can address everyone with "love", "sweetie" or "honey"
    Suggested by @carlastern
  9. Lead with a question about them, as in 'hey! How was the concert? Tell me everything!'
    Suggested by @LaiaPM