The internet is flooded with people finders. They claim you can simply enter the information and *poof* you have all the information you wanted on that person. For a general search, “I wonder where my best friend from primary school lives?“, an online people finder could be a good starting place for you. However, for important and time-sensitive matters an online people finder could be a waste of your time and resources.
A professional investigator like Hawk PI has access to more accurate databases and other resources and can verify the information in a variety of ways, including retrieving evidence that the person lives/works at the specified address, which can be extremely beneficial when serving papers or in child support cases. The costs are more using a private investigator but this is one case where you get what you pay for.