BAW
Yeah, I never knew exactly where they were, because the only source of Information I got were two Facebook pages of participants, and they only posted once a day at late Evening or Night about their previous days. On Saturday I thought they were in Salzburg, so I drove 500km (250km in one direction). However, they were still in Munich. On Sunday they were actually in Salzburg, so I drove 500km again, but I couldn't find them there. As it turned out, I missed them just by a few streets. On Monday they messaged me on Facebook, because I had asked them were they were next, and they told me the exact Hotel in Vienna. So I drove 700km to Vienna and back. But it was all worth it in the end!
The things we do for spotting.

I had a kind of similar but better experience spotting a convoy of Malaysian and a couple Australian vehicles driving through Bulgaria. I took a train to Sofia and searched for them for quite a while but I got no replies about their location. A couple of days before they contacted me telling me which day they would be in Sofia so I still had hope. I ended up staying overnight in a hostel in Sofia and, since I was hunting for one anyway, buying a car in Sofia the next morning.
And thankfully while I was sleeping I received a message and they told me what hotel they were staying at, so I managed to catch them all in the morning!