Unless the person in question is extremely famous or there is other information entered in the query, the odds of finding him in a search engine with only a first name are next to none. Even by entering both first and last name, it's unlikely.
When typing a name in the search field, also consider where the person is located because this will help narrow the search. Looking for "John" or "David" could bring up millions of results. However, by typing in information like the person's occupation, location and other data, the field can be trimmed to a manageable number of results.