Im pretty sure his caravan doesnt go to Solitude. try Windhelm
also, he might of become 'dislodged' from his caravan but still following the same route so try waiting 9-15 hours outside Windhelm over and over again
His caravan is from riften to dawnstar.. and well what i meant was.. I searched him in the caravan (where he was supposed to be) and well as said he wasent there, then i wentto soltitude as it was the last time i saw him
But i can try waiting in the place where teh caravan normaly is