The first is the Coop site. Both require a paid subscription to get a sitter's details.
(Be aware that it is the responsibility of the dog owner to determine that a carer is compliant with the education requirements under the TSchV.)
Another site that isn't specifically for pet care but has provided useful contacts for many folks is Rent-A-Rentner, a platform tor retired folks who wish to work a bit: http://www.rentarentner.ch
And of course you could always post an ad on the EF market place. But the same caveat as to dog care requirements applies - be sure that the person you hire is compliant.