Pistorius, famously known as the "Bladerunner", is a paralympic winning athlete who recently competed at the 2012 Olympic Games in London.
Police spokeswoman Captain Sarah Mcira confirmed Steenkamp was shot in the arm and head. She died on the scene.
Shiri Reouveni, of Capacity Relations PR agency, confirmed to Sapa that Steenkamp (30) had indeed been killed. She said a statement would be issued later.
Steenkamp was born in Cape Town, grew up in Port Elizabeth and resided in Johannesburg. She studied law and was popular as an FHM cover girl who was named the first face of cosmetics giant Avon South Africa.
According to media reports, Pistorius mistook Steenkamp for a burglar. He allegedly shot her four times and Steenkamp was declared dead on the scene.
Steenkamp was set to star in the Tropika Island of Treasure Show scheduled to be broadcast this Saturday on SABC1. According to Tropika's website, Reeva had travelled between Johannesburg and Cape Town to shoot some of SA’s leading campaigns and commercials.
"With a background in TV presenting, once the live roaming presenter for FashionTV in South Africa, Reeva is currently working on some major projects that include smaller TV roles, as well as a lead in a new reality TV show. Reeva has a passion for cars and cooking and prefers to read a book on her off days and spend quality time with friends and family."
Pistorius and Steenkamp were first spotted at the SA Sports Awards last year. At the time, Steenkamp claimed she and Pistorius were just friends.
Media personalities react to alleged Pistorius shooting
Model Lee-Ann Liebenberg tweeted that she was absolutely shocked and heartbroken, while model Ryan Botha said he was sad to hear the news. "How tragic. My thoughts and prayers are with Oscar and both their families," he said.
Publicist Farah Fortune tweeted : "I just heard about Reeva Steenkamp. I'm in shock. May her soul rest in peace. I can't believe it."
Top Billing presenter Jo-Ann Strauss tweeted: "So sad for Reeva Steenkamp's family and for Oscar Pistorius. This highlights how unsafe most South Africans feel because of crime."
Presenter Sade Giliberti said: "But guys then you also have to think. How unsettled are we? We hear a noise, we freak out, we shoot! That's a state of mind."
Actress Terry Pheto said: "This is Tragic!! My heart goes out to both families. Sad how one's life can change in a minute."