In the case of a 30yo adult male, if you filed a missing persons report with the local police, what action would it be reasonable to assume they would take?
The first steps probably vary depending on the area you are in. First the police will get the basic information as part of the missing person report. If they have reason to believe foul play is involved, they will probably ask your permission (assuming you have the right to give such permission) to use publicity to find the person.
Afterwards, all information is linked to a national computer linked system in case this person is found, or information pertaining to the missing person is come across (i.e. license plate involved is ran, blood type at a crime scene, arrest of individual).
I apologize that my information is pretty basic, but it should be enough to get this thread started for you.
You would probably have alot better luck with a private investigator, IIRC a hefty portion of “missing” folk just up and ran screaming from unhappy relationships and rarely constitute any criminal legal problem.
That is my understanding too. I guess what I am asking is would the police do things like checking the morgue or hospitals? Would they inquire of the persons employer when they last came to work? Or would any serious effort to locate a missing adult where no criminal activity is evident rely on the actions of family and friends?
The will call his employer and see if he is at work or has quit his job recently. If he didn’t have a job they might check the morgue. Other than that it is doubtful that they would do anything at all other than file the report unless thier is some reason to expect foul play.
At 30 years old he is an adult and can “drop out” of society anytime he wants. He could be shacked up with some woman, living on the street, or traveling around the world. It’s not anybodies business.
Except the IRS’s, who still wants to make sure they get their cut of any money he might earn. 
It depends on the circumstances involving how the person went missing. What is the background history of this person? Did they have enemies who said they’d harm or kill them? The police would take these things into consideration. And it isn’t necessarily true that the police would do absolutely nothing because the person is 30 years old. Look at all the recent news stories about adults who went missing and the police did investigate and some of them have been found dead. You might try this forum for advice if your question is more than hypothetical, Kolak of Twilo. They could give you solid advice on what action to take, and support. Good luck, if someone in your life has gone missing.
The IRS NEVER forgets…eventually s/he will surface, and returns will be required.