The woman said during two of the incidents her grandmother was sleeping inside the house. "It's been extremely distressing for my nana who is concerned for her safety and so are we.
"She no longer feels comfortable staying in her own home. Whoever is doing this has violated my nana's feelings of personal safety.
"Police are doing what they can to catch the offenders and I urge anyone with any information to come forward before these offenders strike again and the situation gets much worse."
The fires were lit despite adequate security lighting at her nana's property, she said.
Her Facebook posting about the fires sparked reports of similar incidents in the area but some elderly victims told her they were too scared to tell the police, the woman said.
Tauranga Salvation Army home care worker Jessica Shannon said on July 4 someone lit a fire in her elderly client's Winchester Tce letterbox which was reported to police.
She understands other elderly residents in the street had their mailboxes set alight.
Ms Shannon said her client was "beside herself" and felt afraid to stay in her home. "It's disgusting and appalling that someone is terrorising a little old lady."
The client aged in her 90s, who also refused to be named, said a few weeks ago someone also tore her letterbox from its stand and tossed on the ground in her front yard.
"I think it was just a few brain-dead people who have got nothing better to do."
Winchester Tce resident Justin Ansell said his mailbox was targeted during Mother's Day weekend and he and a "Good Samaritan" passerby also put out a letterbox fire in a neighbour's box.
Bethlehem Neighbourhood Support co-ordinator Cathy Hayes said she had been unaware of these incidents, but intended talking to residents of both street as well as the community constable.
Acting area commander Inspector Karl Wright St Clair said police were investigating two incidents of wilful damage to a letterbox at a residential property off Cambridge Rd.
"Wilful damage is not only an offence but can be extremely frustrating for those who become a victim, especially if it becomes a regular occurrence," he said.
"Often security lighting and trimming foliage on your property so that people cannot hide in your yard are good ways of avoiding becoming a victim."
Mr Wright-St Clair urged people to report any suspicious persons in their neighbourhood at any time.
Good neighbours
* To join Bethlehem Neighbourhood Support Group phone co-ordinator Cathy Hayes on 07-579 2040.
* Ring 111 immediately to report any suspicious behaviour or phone Tauranga police station on 577 4300.
* Note down times and car registration numbers where you can.
* Alternatively report suspicious activities anonymously to Crime Stoppers 0800 555 111.