Grig Richters, who co-founded asteroid day and directs films for Films United, wrote in a press statement: “Last week my life was threatened by an anonymous man near Dortmund and the 40 year old VW bus which follows me around has been vandalised in Hanover last Saturday.”

Richters said he was able to remove the offensive vandalism from the van, which has been signed by scores of people writing messages of support. He posted on Instagram: “This could have happened in any city and the police in Hanover treated us with much respect.”

Richters set out on foot from Paris for Berlin on 27 October to campaign for better conditions of unaccompanied minors living in refugee camps in Greece.

Photo: Grig Richters. Images of the graffiti daubed on Richters' bus

Writing on Monday, he said he had already completed 800,000 of expected 1 million steps. On the way, he spoke with mayors of towns including Aachen, Bonn, Cologne and Dusseldorf, who he said are willing to take some of the stranded young people. He expects to reach Berlin on 9 December.

People can support Richters by signing his petition for action in helping unaccompanied minors, which is addressed to German Chancellor Angela Merkel, and/or donating to the “I March For You” initiative.

Click here to see where Richters will visit next.