Seven people aged 22 to 38 are suspected. No arrests have been made.
For months Last Generation (Letzte Generation) has disrupted traffic in German cities and performed stunts like hurling mashed potato at an art work.
Chancellor Olaf Scholz has condemned their campaign as “completely crazy”.
Some 170 police took part in Wednesday’s raids on flats and other buildings in Berlin, Bavaria, Dresden, Hamburg and elsewhere, shutting down the group’s website and freezing two accounts.
The seven suspects are accused of organising a campaign to collect at least €1.4m (£1.2m) in funding mainly to finance “further criminal acts”.
Police and prosecutors said the raids were aimed at establishing Last Generation’s membership structure.
Two of the activists under investigation are suspected of last year trying to sabotage an oil pipeline running across the Alps from the Italian coast at Trieste to Ingolstadt.
Last Generation criticised the raids using the chancellor’s “completely crazy” quote as a hashtag VölligBekloppt, asking when the authorities would instead search “lobby structures and confiscate government fossil funds”.
Another climate action group, Ende Gelände, complained that the raids were targeting people seeking to “raise the alarm about the climate crisis rather those responsible for it”.
Last Generation is campaigning for a speed limit on motorways of 100km/h (62mph) and last week blocked 12 streets in Berlin, gluing themselves to the road or to cars. But these street sit-ins have resulted in some drivers lashing out at protesters.
The group played a key role in protests against the expansion of an open coal mine in the village of Lützerath in January, where campaigner Greta Thunberg was briefly detained.
Last October two activists threw mashed potato at a Claude Monet painting at a museum in Potsdam near Berlin and then glued themselves to a wall, an action that mirrored similar protests in the UK by the climate action group Just Stop Oil.
Last Generation are not limited to Germany. Two activists glued themselves to an area in front of the Austrian parliament in Vienna on Wednesday, defying a ban on protests outside the building.
In Italy, three Italian activists were due in court on Wednesday for gluing themselves to a Vatican museum sculpture dating back to Roman times last August. Activists belonging to Ultima Generazione had also coloured the Trevi fountain in Rome black as a statement against fossil fuels.