LBi was awarded the brief following a three-way pitch against undisclosed agencies.
The site, which launches later this year, aims to take on leaders such as Facebook and YouTube in the social networking field, but with a focus on entertainment.
As well as virtual communities, the site will offer users a range of online film and music clips based on HMV's strong links with music, film and games companies.
Gideon Lask, the e-commerce director for HMV, said: "The HMV social networking site will be an important element in our customer engagement strategy."
He added that HMV is also in the process of appointing agencies for other aspects of the project, including content, marketing and PR.