Eren, who entered Iran on foot via the Turkish border with only a backpack and no security gear, had traveled to the country to deliver donations from the Stuttgart region, Südwestrundfunk reported.
In a post on Instagram, STELP confirmed the organization has lost direct contact with him and has contacted Turkish authorities, as Eren holds Turkish citizenship.
The group urged the public to refrain from speculation, saying it could compromise his safety. SWR reported Eren traveled without a helmet or satellite phone to avoid being mistaken for an agent or saboteur.
Iranian Foreign Minister Abbas Araghchi on Thursday confirmed that Franco-German cyclist Lennart Monterlos, missing since June 16 while traveling in Iran, was arrested for "committing a crime" without specifying the charges, in comments to French daily Le Monde.
Araghchi said an official notification was sent to the French Embassy regarding his situation, without providing further details.
“It’s a worrying disappearance, and we are in contact with the family,” French minister for citizens abroad Laurent Saint-Martin told RTL radio.
“It is worrying because Iran has a deliberate policy of taking Western hostages."