The deal marks the second tie-up between the world's biggest automaker and a software company in as many months.
Toyota and Microsoft last month announced plans to bring Internet-connected services to Toyota's cars across the world.
"Social networking services are transforming human interaction and modes of communication," Toyota President Akio Toyoda told a joint news conference with Salesforce.com CEO Marc Benioff in Tokyo.
"The automobile needs to evolve in step with that transformation," Toyoda said.
Information technology and telematics are expected to play a key role in adding value to future cars, and become a marketing tool as consumers look for connectivity not just from their laptops and phones but also with their cars. Toyota has already developed its own telematics service to connect it with drivers and dealers.
Under the new private social network, called "Toyota Friend," owners will be able to "chat" with their Toyotas like they would with a friend on Twitter or Facebook.
The car would have its own "profile" and send a message to the driver's phone, for instance, reminding him to recharge its depleted battery. The owner would be able to carry out a simple, two-way conversation with the car.
The service would be an extension of Toyota's network to be based on Microsoft's Azure cloud computing platform that would give customers across the world access to Toyota's digital services such as GPS and multimedia.
Customers will be able to extend the private "Toyota Friend" network to include their family and friends through public social networks such as Twitter and Facebook.
The service will be offered first in Japan with Toyota's first battery electric vehicles and plug-in hybrid cars due next year, Toyota said.
Cloud-computing, one of the fastest-growing areas in the technology sector, refers to the use of remote data centres to deliver software, data and computing power.
