One member of St John's Church, Isoyama, has been confirmed dead but there has still been no news of the tiny church's other seven members.
"We pray that they are all safe in some temporary shelter," said Bishop Kato.
The diocese's main church, Christ Church Sendai, has still not been able to locate some of its members.
Despite being on the coast, the tsunami did not reach the Grace Church and kindergarten in Kamaishi, but not all members have been found, the bishop said.
Around 450,000 people are living in temporary shelters. Bishop Kato said that food and petrol supplies remained low, while gas, electricity and water services were still out in many places.
"The tsunami and fires it caused have made us miserable," he said. "We were simply not prepared for problems on this scale."
The bishop also expressed concern over the worsening nuclear situation as efforts to cool down reactors at the stricken Fukushima Daiichi plant were stepped up. Authorities have enlisted helicopters and water cannons and it is hoped electricity will soon be restored to the plant.
The Diocese of Tohoku has set up a relief centre at its diocesan headquarters in Sendai to coordinate the church's humanitarian response. One of its most immediate tasks is to confirm the safety of parishioners and church buildings.
"The eventual challenge is to rebuild our diocese. With God's blessing I pray that we will accomplish this task," he said.
"I realise that many challenges lie ahead of us. I pray that what we do will be with God's blessing that Christ has taught us to do so in his holy words."