Andrew Thompson was taken to Frankfurt by his mother, Melinda, in 2008 when he was three and has not been seen by his father Ken since.
Police and Interpol efforts to find Mr Thompson’s estranged wife and child failed so he decided to hunt for them himself.
Melinda once worked in London so his two-wheeled search began in the UK but after finding nothing he moved on to other countries including France, Belgium and Germany.
Last week he received an anonymous email saying his son, now aged six, was in Amsterdam and the tip-off proved correct.