@MinnaGG It sounds like the game is assigning a true non-player character as the target, instead of an inactive town resident. NPCs are role sims like maids, repairpeople, babysitters, pizza deliverers, etc. and don't live anywhere in town. (If they were moved into a household, they'd lose their assigned role.) The game also sometimes generates homeless coworkers for your active sims; these coworkers appear for their work shifts but then drive off the map into oblivion afterwards. But either way, they're not going to exist anywhere on the map unless they're performing their assignment, or unless the game randomly pushes them to a community lot.
If your sim doesn't already know the target, I'm not sure what you can do to make them show up on command. You could check the relationship panels of the other sims in your household; maybe you'll get lucky. (As a shortcut, you could prompt your sim to throw a party; all household acquaintances will be listed in alphabetical order, and hovering over a name will show which household sim has the highest relationship with each potential guest. You could then just cancel the party interface.)
Otherwise, there's not much you can do without mods. Plenty of opportunities are broken in TS3, and most of us just sigh and cancel them, annoying as that may be.
Ok, well thank you for explaining. I've tried the party thing and nothing. Guess I'll have to accept that it's just not going to work. Thanks for your time, I appreciate it!
