Are you looking for help coding it, or just some advice on how to go about it. I run a site that's kinda like a punk myspace at punx.com . I use phpfox, and I host it at dreamhost.
why dont you just purchase phpfox ok its not the best but its probably the best one out there which you could then modify to make it better
if you want someone to code this for you, i hope you have some money to toss around. honestly i know a handful of developers but not one would do it for less than $10,000. so like others have stated, your best bet is to purchase a commercial social networking script. just thought that i would give my opinion on this. also, you may want to look into purchasing a server or two if you are serious about this. no guarantees that it will take off... but if it does, you'll be glad that you have them.
The basic phpfox is good enough. I have one site using phpfox 1.1, I am still waiting on 1.5 to become stable.
If you want any one to just help you, you obviously don't realize what a time commitment it would be expect to pay ALOT of money if you want to get this custom done noone will spend months pouring over millions of lined of code for free this site is running phpfox http://www.emoscene.com/
custom script like myspace go for 2k to 10k. Depends on what you want. then you have to be careful someone not given you premade myspace clone.