How are social networking sites appraised?

For instance, if you have a social networking site with 1 million active users, will it be valued based on a dollar amount per user? If so, what is a reasonable dollar amount per user...$5, $10...?

Your thoughts...

Well apparently each Facebook user is valued at around $70, if you measure it like that. (750 million users, valued around $55 billion, give or take.)

I'm writing a business plan to present to some investors and I have to come up with some enticing value projections, ones that are also credible and feasible to attain.

I have to explore the entire criteria for assessment. I just figured that user-base will be one of the main factors to take into account.

Thanks for your input

I'm sure many other factors come into play. I hate to reference a movie for business advice, but when Eduardo was pitching to execs in The Social Network, he mentioned duration of visit, frequency of visits, etc. Naturally, having a site with 1 million actively engaged users will be worth a lot more than a site that's been dead for 5 years, even if it's got 1 million users.