It’s a tale of two social network developer platforms. Hi5, a site popular in some Spanish-speaking Latin American countries and other regions around the world, launched its platform at the beginning of this month — and the third parties that have applications on the site are reporting impressive growth.

Leading widget company RockYou, for example, says its “SuperFive” application has already been installed two million times in the last couple of weeks. Why? Hi5 specifically offers ways for users to contact each other through third-party applications.

Meanwhile, applications on market leader MySpace’s platform have been seeing insignificant growth since it launched in mid-March — because MySpace has yet to introduce effective ways for applications to contact users. However, one top developer tells us that MySpace will soon be offering notifications, email messages, and other so-called “viral channels” already available on Hi5.

So MySpace may soon become the hot spot for applications that third parties have long hoped for. Meanwhile, Hi5 may have done a better job of addressing the spam problem.

Does “viral growth” = spam?

To get an idea of what I mean by “viral growth,” here’s a closer look at RockYou’s “SuperFive” application, which lets users send action messages like a “hug,” “tickle,” etc. to Hi5 friends. If this sounds familiar, it’s because 1) Hi5 already has a feature called “five” which is basically a copy of Facebook’s “poke” feature and 2) RockYou and competitors already offer Facebook applications where you can hug/tickle/poke your Facebook friends

I’ve been hearing that this messaging feature is actually useful for companies that want branded contact with users, like being able to “throw a Coke” at a friend (I made that example up, but you get my drift). Many developers have made good money from selling branded pokes/hugs/tickles.