hi5.pngFacebook rival Hi5 says it is working on its own developer platform today, the latest social network to realize that it had better open up quickly or potentially lose customers to more active pastures.

The San Francisco company announced the move at the CommunityNext conference, for developers who build applications on social networking platforms.

Back in May, Facebook launched a platform for letting software developers build applications within its site. The move has kicked off a wave of excitement. It has created serious concern at MySpace, LinkedIn, Bebo and other social networks.

There are at least four conferences in the Bay Area alone this month on the topic of platforms.

Hi5 is around the same size as Facebook worldwide, with more than 35 million active users on its site, according to recent Comscore data.

While Facebook is growing quickly around the world, the majority of Hi5’s users are already located outside of the US. Hi5 is known for reconnecting immigrants in a new country with long-lost friends and family members back in their home country. Such differences between user bases have an impact on what sort of applications are developed for the respective platforms. Its easy to imagine a Hi5 application, for example, that lets users find other people from their hometowns who now live in their new community.

Hi5’s executives told me today that they are getting feedback from its users and third party developers about how to prepare the platform.

The company already lets users embed Flash widgets developed by third parties, similar to Myspace. It has also developed more advanced features of its application programming interface (API). It is currently giving access to select widget-makers, including Slide and RockYou.

Hi5 hopes to have a platform ready for general use within the next twelve months.

Slide and RockYou, rivals for the crown of Widget King, both recently told VentureBeat they expect to capture the third-party application market on Hi5, Bebo and other social networks when these networks launch their own developer platforms.

They cite their experience building Flash widgets on Myspace and other social networks, and building applications on Facebook, as impetus for their success on new platforms.

However, some smaller companies are also doing quite well. Several one- and two-man teams of developers of Facebook apps say they’re making more than enough money on Facebook to support themselves. They’re doing so in part by using the existing Facebook ad networks. Some are looking for angel or VC investment to grow more quickly, but say they can survive without it.

Other upcoming Facebook conferences in the Bay (that we know about) include:

Graphing Social Patterns

App-Camp

SNAP