“Have you spotted any celebrities?”
Your friend recently moved to a large city. You are talking to her about her experience living in a larger city. You want to ask her if she's seen any famous people.
Have you spotted any celebrities?
Asking "Have you...?" is better than "Did you...?" when you are asking for general news about a person's recent life:
Have you lost weight?
Have you seen "Avatar" yet?
Have you called your mother lately?
You use the word "spot" to describe seeing something that's rare and difficult to see.
A good example of "spotting" is "bird-spotting", which is a hobby for some people where they try to see & identify different types of birds.
Another good example of "spotting" something is spotting a celebrity in a large city.
"Celebrities" are people who are famous nationally or internationally. They include movie and TV stars, musicians, etc.