Finding out the basics about a person is typically done through some computer research. This includes running names through databases. By doing these computer searches, an investigator can quickly get the basic information they need to begin their information gathering. These searches can provide records of criminal history, phone numbers, vehicle information, and other information that can help turn a name into a person on the investigators side.
The detectives may choose to engage in a little footwork and confirm important information that the search provided such as income and employment verifications. They may visit people that have known the person recently or from the past. A lot of this work is done on an "undercover" level as they dig deeper into the personal information about a person.
There is also the basics such as actually following an individual and using physical surveillance. Photographs are often taken to provide proof of their findings. Video cameras , cell phones, and wire taps can also be used to collect hard evidence.
As you can see the range of methods that are at a detectives disposal are wide, as we have only touched on the most common ways of gathering information. How a detective approaches a case depends on they type of case and the position of the individual being researched. There is nothing shady or any reason to be skeptical of hiring a private investigator as they follow rules and codes of not only their own but those set forth by the government.
There is no reason to hesitate if you feel a need to find truth or lost individuals as this business is clean and can help bring a sense of serenity to the troubled heart or mind.