[Social Engineering] Find a specific person in a foreign city (Known Individuals)

[Lamech]

I would use something akin to the MH2 rules for investigation.

A thing to note:
You need enough info starting out to uniquely identify one person. Not half a dozen. Not zero.
This list:

Originally Posted by vicky_molokh

• A semi-correct/semi-erroneous facial composite drawing of the character. Notably, race (which is characterised by skin, eye and hair colour) is grossly misjudged. However, height, sex, age etc. are correct.
• A phone number, which is by now obsolete, because the NPC either gave away or thrown away the SIM card, and now somebody else has it. (This is likely a chance for the face or investigator to get the most spotlight.)
• Perhaps some info on the NPC's interests/hobbies, which might give an opportunity to figure where else to look.
• Sure knowledge that the NPC speaks a specific language fluently, and knows a specific Cultural Familiarity. (This is a small clue - the town is a melting pot, but the listed CF/language combination are reasonably common there.)
• (For one PC only.) A dubious but actually true name, upon hearing which the NPC will drop suspicions and talk. (Not the NPC's current fake name; this clue is pretty important, and only makes sense in context, but the point is one PC can perform this check, but will likely not rely on it.)

Will make it all most impossible. You've given them bad info. It points to someone who does not exist. Now there is the magic name thing, but is the guy going to drop all pretense if a group of people start blabbing around town? If the party asks seven people if they are "the real slim shady" will it work when the "real slim shady" is number 8? Assuming the party needs to be sparing with the name, they'll have problems. (If they don't need to be sparring with the name, they can simply post an ad in the local paper asking "will the real slim shady please stand up?".)

What might happen: So the party makes a list of people with the same hobbies/language/CF as the target. They track down the phone and figure out where it came from. Our target "slim shady". He doesn't match the description. They ask him where he got the phone. He gives them a plausible dead end that goes nowhere. Party continues to search for someone who matches the description. After an exhaustive search they conclude that nobody in the city matches the information given.