Writing on Facebook today, the health and detox coach said: "Tragic news my girlfriend died in a scooter accident we had today.
"I am in total shock as I've lost the most precious person I had ever connected with. My brain keeps going into denial...I am distraught. She was also pregnant so I lost my child too."
Rose was from Blackpool but moved to Chiang Mai in Thailand with her boyfriend and son, Shaye, 5.
She gained fame for her YouTube videos that showed her breastfeeding her son and encouraged women to do the same.
Rose spoke to UK breakfast TV hosts Phillip Schofield and Holly Willoughby on This Morning about her cause, saying she wanted to "normalise breastfeeding older kids' and "expose it until it becomes part of normal reality".
Her YouTube channel Sophie's Joy Breastfeeding Mama amassed more than eight million views.
Her last video, posted the day before she died, shows John, Shaye's father who lives in Bangkok, spending time with them in a hotel pool and at a water park.
She began posting videos to the channel a year ago and has amassed 32,000 subscribers. One video of her breastfeeding Shaye attracted 25 million viewers.
In her videos she also promoted her son's raw vegan diet and was a supporter of home-schooling. Rose was six months' pregnant at the time of the crash, according to Lieutenant Colonel Sanit Nookong.
"Witnesses said the motorbike was travelling in the left lane northbound and pulled out to drive around a parked car, and was struck by the truck."
"The woman was then run over by the truck and sustained fatal head injuries."
The crash happened just after 12.10pm local time on Monday.
It is believed the lorry driver, a 30-year-old local man, handed himself in to police after initially fleeing the scene.
Rose had touted the health benefits of breastfeeding children, and said it was a good way to physically let your child know "that you are there for them".
She also argued that breasts have been over-sexualised in modern culture and we should not feel squeamish about them being used for their natural purpose.
However, her health claims were called into question by medical experts, who said that although the milk will not harm older children, it is also unlikely to provide benefits.