Locator Agents
Someone needs to add more useful information here, formate it nicely and put it in the right category (as I don't know how to do that).
Locator agents are regular NPC agents that offer the special service to locate another player character. You can find locator agents via: [1] check the box "Location Service". You need the standings to access the agent to use its location service.
When you talk to the locator agent, you will have a button to locate a character beside the request mission button. You have to type in the name of the character and the locator agent will give you a quote how much it will cost (Note that the lower the price the closer the target player is to your location, so you can determine without paying money whether the target is in another region, just another constellation or in your system [if it's the latter I doubt you will keep the ship you are flying for long]). The locator agent will then run its location service which will take a couple of minutes, depending on its level (the higher the level the faster he runs). Once done the locator agent will send you a Notification with the location of the target which will include the system, constellation and region as well as the station the player might be docked at (Note that you see that the target is in space when there is no station). E.g. "The sleazebag is currently in the Bukah system, Nohshayess constellation of the Khanid region." Note that a lvl.3/4 locator agent can find people in wormholes as well, though that's of limited use: "The sleazebag is currently in the J215736 system, Unknown constellation of the Unknown region." Yay.
The target won't get any notification that he has been located.
The range of the locator agent in which he is able to detect players depend on its level.
lvl. 1: Constellation
lvl. 2; Region
lvl. 3: Everywhere
lvl. 4: Everywhere (but does it faster than lvl. 3)
Afterwards they cannot be used for some time (I am not sure if the time it takes depends on the level, my lvl. 4 agent was back after 30 minutes).