How about police work? Talk to friends and family, follow people, investigate. Stake out the homes of known associates. Leaving motorists the heck alone ought to free up all kinds of resources for this kind of activity.
Many agencies have units sets up to search for the most serious felons with warrants, we do and random traffic stops is not one of their tactics. The reality is that in large cities, those with felony warrants outnumber police officers 15 to 1. Unless they pose a significant risk it is simply assumed that they'll turn up eventually by either being caught committing another crime or during a traffic stop. We are not allowed to randomly stop whomever we want and demand ID. We are allowed to conduct stops of vehicle traveling on the people's roads for believed violations of the peoples traffic laws.