Slawomir Sierakowski, a Polish political commentator and editor in chief of "Krytyka Polityczna" ("Political Critique") monthly magazine, wrote the letter to Azerbaijani President Ilham Aliyev urging him to release the bloggers.
Emin Milli and Adnan Hajizada were sentenced to 2 1/2 and two years in jail, respectively, last month on hooliganism charges following a scuffle in a Baku restaurant in July.
International human rights organizations consider the case politically motivated as the two had written critically about the government.
"It is the Azeri people themselves who can bring about some real change in their country," Sierakowski told RFE/RL. "But of course, international pressure is something that played a big role when Poland was under repression. Therefore, we must keep on writing such letters."
Asked if there was anything he would tell Hajizada and Milli, Sierakowski said that, paradoxically, their jail time might spark further actions across youth democratic movements rather than scare off potential activists.
"I would like to invoke Jacek Kuron [prominent communist-era Polish dissident], who was imprisoned for nine years and who said that nothing serves better for further social engagement than imprisonment," Sierakowski said.
"Let them know, let them have the satisfaction, that their time spent in prison is a breakthrough and is important for their self-organization. I can only hope that those who are free will manage to use their experience to serve well in this case. The bloggers can be proud of themselves."
Sierakowski was among those gathered at a central Prague cafe on December 10 for the International Letter-Writing Marathon. The event, organized by Amnesty International in Prague, saw a group of young activists handwrite urgent appeals for prisoners of conscience all around the globe.
Skeptics have asked what difference letter-writing can make to the plight of individuals jailed by authoritarian regimes that are often resistant to foreign pressure. But Matt Gregory, coordinator of Amnesty's English speaking group, said the point is to "give voices to the voiceless."
"Many times prisoners think that no one knows about their plights and what's happening to them. Governments act as if no one knows what they are doing," Gregory said.
"The letter writing does the job of bringing attention to these issues and cases. There have been multiple examples of letter-writing being one of the reasons that got prisoners released."