Free English classes for new migrants were also recently added to the list of services after fundraising to hire a tutor.
Mrs Warren said the theft happened while one of the volunteers was busy grabbing a coffee.
The normal protocol was to lock the cashbox but it took only a few seconds for the brazen thief to snatch the box and flee the store, she said.
"The volunteer concerned is naturally very upset but we do realise these things do happen from time to time. It's very disappointing as our trust is a social support enterprise which works hard to assist people who need some help to find practical solutions to their problems."
Mrs Warren said the Merivale Chirp op shop opened only last July.
"We are still trying to build our resources up. The cash stolen may not sound much but it's a huge loss when the trust struggles to pay the $500 rent, power and rates each week."
News of the theft has spread around the community, prompting one man to donate $150.
Mrs Warren said she would love to hear from anyone willing to volunteer in the store, donate items or money, or possibly offer to tutor the trust's clients.
Anyone with information about the theft can call Tauranga police on 577 4300.