Bishop Gore School student Nyah James was discovered on Monday at an address in the Blaenymaes area of the city.
She was described as a "beautiful vibrant" child with her whole life ahead of her by her family.
Police said action will be taken against those "who post messages that are abusive, threatening or insulting".
"We would urge young people to be responsible when posting online and think about the consequences of your messages and how they may impact on others," said a force spokesman
Officers are continuing to investigate her death, and renewed an appeal for anyone with information about the teenager to contact them.
South Wales Police has warned people to consider the impact of social media messages following the death of a 14-year-old Swansea schoolgirl.