When you run out of ideas for guild events, copy television? Works for me!
I formed two teams of four players. The objective was to solve the clues and get to each pitstop first. The team arriving first got 20 points, and the other team would get 10 points. I parked my alts at all the clue locations (I have multiple accounts and two computers though, you might need help with that part).
I handed out matching shirts and fun gray item hats to each player just for fun and so they could keep an eye on their team. So we had team blue and team orange.
The rules: no class portals/summons of any kind, no mass summons, no help from anyone not on team, no looking at guild roster during contest (because it would giveaway location of hidden guildie), no website help. Allowed: hearthstones, city/zone portals, using the map.
I would mail or whisper/say each clue to the team leader. Each team was in a seperate vent channel to discuss the clue. I would jump into each channel to check on the status of each team. Here is an example of a clue:
5 Paths, One peak, find Illayeria East of the Retreat. (Sun Rock Retreat, Stonetalon Mountains)
After ten minutes, if no one was close to the location I would post a screenshot on our guild facebook page. Here is a shot of the first location, which set the pace for the contest:
Team Orange got ahead in the beginning and won every pitstop except one. The last pitstop was very close though. The winners received a choice of bloodthirsty PVP crafted piece or epic enchant/embossment.