It's possible that:
* The name is misspelled: Double-check the spelling and try searching again.
* The person is not a prominent figure: If they are a relatively unknown actor or behind-the-scenes personnel, they may not have a public online presence with readily available information.
* The person exists but is not in entertainment: There might be a person named Gillian Vanderburgh who is not involved in the film or television industry.
If you have more information about this individual, such as a specific role they played, a production they were involved in, or a time period they were active, it might be easier to find information about them.