Mark CMG
Creative Mountain Games
Have the PCs decide where they all are in a city or town then have the first witness a crime, something stolen, and the victim shouts, "Fifty gold to the hero who catchs that thief and the same to anyone who helps him!" Then wind a way through the city making sure the thief runs past each location so that the party can meet in transit. Maybe have a couple of ther NPCs running along for some of the time losing their breath or legs at just the time when it would be convenient for them, before collapsing, to quickly explain the chase to a new PC. Make sure anyone who has a definite stopper, like a spell or net, is last on the trail you weave. It's a bit of a twist on The Three Muskateers rallying scene which might also be used under other circumstances.