In 2018, Thunberg's school strike grew into a global movement that became known as #FridaysForFuture.
Millions of people in countries such as Australia, Ghana, Germany and the UK have taken part in the protests.
She said on Instagram that people had tried to sell products and collect money in the movement's name, the BBC reported on Thursday.
"My name and the #Fridaysforfuture movement are constantly being used for commercial purposes without any consent whatsoever," the 17-year-old activist said.
Thunberg has also applied to trademark Skolstrejk for klimatet (school strike for climate), the phrase used on her protest sign that she has carried around the world to #FridaysForFuture protests.
She added that people had tried to impersonate her "in order to communicate with high profile people, politic, media and artists".
Thunberg also announced she has set up a non-profit foundation to handle the financial side of #FridaysForFuture.
It will manage money raised from donations and book royalties.
"The foundation's aim will be to promote ecological, climatic and social sustainability as well as mental health," she told her Instagram followers.
Thunberg has become a strong voice for action on climate change. However, her message on tackling rising temperatures has not been well received by everyone.
Earlier this month, US Treasury Secretary Steven Mnuchin told the teenager to go away and study economics before lecturing investors.
Last December, she was named Time Magazine's Person of the Year.
( With inputs from IANS )