Tips for a massive city manhunt.

Hello. Recently, my party has arrived in a city and a festival just happened. A friend to the party so happened to be running a game of Tag a Guard that he decided to totally change. A massive advertising campaign the first morning of the festival later and he has thousands of people, young and old, trying to win a pot of gold. Their only goal? Tag the party before noon (2 hours).

I have a baseline for how this will be ran, but most of it is more of a skeleton than a plan. Does anyone have any ideas for how to handle this? Tips for what to prepare for, tactics I can use, mechanics that would be fun, or anything like that? The party already knows no violence or property damage, they can't enter buildings, and certain spells like flight and invisibility have been banned (for good sportsmanship). I am aware that some of the party intends to hide on roofs, and most of the horde are children.

Additionally, (don't tell my players), this so called "friend" has prepared a familiar and a special casting of locate creature to constantly be tracking them and relaying the information (but only to anyone who goes back to the starting point).

I imagine it would be something along the lines of a skill challenge. They name a skill, you set a DC, and let them roll it, and narrate the results, and they can't use a skill twice. After a set number of successes or failures, they are caught or they win. Additionally, you could make a random table that you roll on after a set number of skills to make things interesting.

Dnd rules for individual combat/actions dont work well in large populations.  Say the party hides, and 40 people are within range to roll a perception check. Youre probably going to get two people who roll 20's and spot the party. 

There are some rules for handling mobs. But i dont know if they handle mob hide and seek.

You could maybe simplify it to the party rolls one stealth and the mob rolls one search.

But honestly, i dont see this realistically being a winnable situation unless the party hides in a pocket dimension or uses other magical means to stay hidden.

The fact that the guy who set this up is essentially cheating would make me doubly concerned if the party spent a lot of time trying to achieve the impossible, only to inevitably fail to a cheating npc, all together which might make some players feel a little railroady...

You're thinking too rules as written. This isn't a combat encounter, this is a story event. The environment. They are meant to win because a rogue with 11 acrobatics can very likely escape a horde of children. Subsequent dex checks to avoid, stealth to hide, and ingenuity. I get it isn't rules as written, but I'm looking for ideas, not how to run it.

Tip #1 : You don't need to keep track of all the participants. Instead I'd suggest running this like a series of random events as one or more participants encounter the party. 

Tip #2 : Have variety in the participants. Nobody said participants are just commoners running around looking. Consider:

• A group that have one or more hunting dogs to help them.
• A group trying to use potions / magic scrolls to cheat.
• A local Artificer who has brought a Decanter of Endless Water to flush them out.
• A street thief / urchin who knows secret passages through the city.
• A group of cowboys riding horses with lassos

If the people are able to find out where they are then there are some things I would aim for:

• The longer they stay in one place, the harder it is for them to stay hidden.
• Word travels. Someone who goes to the home base hears they're in the belfry, and shouts it. Within minutes, all across the town, cries of "The Belfry!" can be heard. The party will hear it too. This should telegraph that they are being tracked.
• People will surge in waves. You can look at a plan of the town, and when the cry is heard and everyone surges to the Belfry, there's a wave of people that the party has to sneak through in order to find a new hiding spot. If they are seen, the cry goes out, and the surge moves toward their new location.
• When the surge arrives at the hiding place, if they find nothing, they will start to spread out until someone reaches home base again and gives the shout.
• Halfway through, someone will have the bright idea of staying at home base and shouting out updates (I'd make the thing ping every few minutes, instead of constant). The party can interact with this as they please - non-hostile spells like Silence, or by shouting contradicting instructions, that sort of thing, but that's up to them!

How you run it also depends on if the party split up, or if they stay all together.

In a split up scenario: Have each member describe how they are hiding, and roll and appropriate check. Then each "round" roll a die to determine which of the player characters has a random encounter with the searchers. They get 1 minute of scene time before you roll for the next encounter. Then keep skipping between the different scenes each getting 1-3 minutes each.

In the stay together scenario: Have the party set out their plan, then have each of them roll a die (d6 or d8 depending on the number of players) and if any of them roll a 1 they have an encounter, otherwise X time goes by without they getting found. 

I would run it like a "chase" scene, where the players and the pursuers take turns making one attempt to escape / catch up. Forget about combat mechanics entirely and simply make very basic statblocks (or reference cards) for each type of pursuer with the key information. Make large-scale a top-down map of the city, and plan a bunch of different reasonable obstacles to run like skill challenges or like a series of puzzles.

For example here's some potential chaser cards:

Kids with Dog
Strengths: 
Keen Smell : Adv on Perception/Survival checks using scent.
Small & Scrawny: Automatically succeeds on checks to squeeze through small spaces.
Weaknesses:
Misbehaviour: Easily distracted, fooled, or bribed. Can be caused to argue with each other.
Inexperienced: Automatically fail checks to use complex equipment/tools.
Dice Modifiers: (unspecified modifiers are all +0)
Skills: +6 Survival, +4 Perception
Saving Throws: Dex +2, Wis -1.

Woodsmen / Woodswomen
Strengths: 
Tough as Nails : Adv on Strength and Constitution checks against non-magical hazards.
Determined: Automatically resists bribes, distractions, or attempts to exhaust / wear down.
Weaknesses:
Straight forwards : DisAdvantage against realistic illusions, and on checks to find secret passages.
Out of Place: Always tries to follow the most direct route (as the crow flies), easily gets lost in back alleys or twisty urban roads
Dice Modifiers: (unspecified modifiers are all +0)
Skills: +6 Perception, Athletics +5, Acrobatics +4
Saving Throws: Dex +3, Str +4, Con +6, Int -1

Farmers / Farm labourer
Strengths: 
Mounted : Automatically succeeds on any speed-based challenge while on the ground.
Handy: Advantage on checks to use non-magical tools / equipment
Weaknesses:
Competitive : May attempt to sabotage rival chasers
Suspicious: Easily frightened / distracted especially by magic
Dice Modifiers: (unspecified modifiers are all +0)
Skills: Athletics +8, Perception +2, Animal Handling +8
Saving Throws: Str +5, Con +4, Wis -1

And here's some potential challenges:

Tannery
Hazard: Stink! Anyone in the tannery must make a DC 12 Constitution save at the start of each turn, on a failure they had Disadvantage on everything they attempt that round.
Obstacle: "Water" Pools. Anyone traversing the tannery must navigate around many large slippery tanning pits / pools. Suggested Rolls: Dex save, Acrobatics.

Stable
Hazard: Flying Hooves! Anyone in the stable must succeed on a DC 13 Animal Handling check at the start of each turn, on failure they have Disadvantage on everything they attempt that round. 
Obstacle: Hay Stack. A good hiding place, but otherwise must be climbed up to reach the roof. Suggested Rolls: Athletics, Acrobatics.

If they are chased run it like combat 

In stead of linear thinking, the towns people are all gathered and bet on the results.  The event has organized special hunters to find and capture/kill the party.

Use the movie running man that stars Arnold Schwarzenegger.

Quote from Character77006 >>

In stead of linear thinking, the towns people are all gathered and bet on the results.  The event has organized special hunters to find and capture/kill the party.

Use the movie running man that stars Arnold Schwarzenegger.

Other potential inspirations:

• the board game Scotland Yard, and all its successors. Have the party periodically required to reveal their location if they haven't been caught yet, via an elementalism cantrip or the like
• the movie Battle Royale, where the party is required to be in specific neighborhoods at specific times