Prominent movement leader Joshua Wong and others recalled in an open letter published by top-selling Bild daily that Merkel grew up in the communist police state of East Germany.
“You have first-hand experience of the terrors of a dictatorial government,” wrote Wong, who was temporarily arrested last week over the protests, and others.
“The Germans courageously stood at the forefront of the fight against authoritarianism during the 80s,” they wrote, stressing that they share the same democratic principles.
We appeal to you as Chancellor of Germany, a country that promotes freedom of expression and human rights, and we hope that you will express your concern about our catastrophic situation, and that you will convey our demands to the Chinese government during your stay in China.”
They also warned that “Germany should be on its guard before doing business with China, as China does not comply with international law and has repeatedly broken its promises”.
Merkel on Thursday starts a three-day trip to China, a major trade partner of the biggest EU economy, with a large business delegation in tow.
Hong Kong has endured dozens of sometimes violent pro-democracy protests triggered by opposition to Chief Executive Carrie Lam's bid to push through a law allowing extraditions to mainland China.
The protests have evolved into a wider democracy campaign involving clashes between protesters and police, in the biggest challenge to China's rule of Hong Kong since its 1997 handover from the British.
China has responded by ramping up threats and intimidation, including by warning its security forces could intervene.
The authors – Wong and the Hongkongers in Germany Concern Group – argued that they face “a dictatorial regime” applying violent measures “with a tendency towards a new massacre such as that in Tiananmen Square.”