I started to look online for platforms, initiatives, databases, that we could use to reach out to new volunteers (coaching/organizing) or participants.
betterplace.org
They offer donation campaigns but also a database for donating time.
I created an ad for coaching at our events: www.betterplace.org/v40005 and for helping out with organizing events and the community www.betterplace.org/v39979.
I also found some old-school volunteering databases like http://freiwillig.berlin. Let’s see if I feel like filling out the WORD document form… 
Let’s collect ideas and ads/partnerships here.