Good question. I've worked with many different startups that struggle with this same question and I sat on the advisory board of a (now defunct) social media startup that was focused on sharing photos of high school sports events that sadly never actually solved this exact question properly.
While I think that you have listed all of the relevant metrics that most financial analysts and investors use to analyze social networks like Facebook and Twitter above, I think that you are likely going about this process the wrong way.
You need to define:
1) What is the mission statement and purpose of your company?
2) How is your company going to generate revenue?
You need to define these two items on day 1, -- though in many cases they will change over time (Apple used to be a computer company -- now they primarily sell phones!). Once you've got both of these answers crystal clear, you can determine what metrics that you believe you should be measured against and what your definition of success would be. It will be different depending on the specific goals of your company. For example, I suspect that one of the early metrics for Instagram was the number of photos shared on the site per day or per month. The social media site that I was involved with never figured out the answer to #2 above -- and though they went through multiple rounds of funding, they were not able to succeed because they didn't have any real business model except "getting acquired". Ultimately, later stage investors balked at investing in a pre-revenue company that had a high valuation and no real business model.
You should create a "benchmark" of what you think your company's most important metric shouldpitchn 6 months or one year and then manage and measure to try and achieve that goal. Though it is early days, I would also create a financial metric that shows some kind of progress on the revenue front -- this is important because it shows that there is a real value to the service that someone (advertisers, users) is willing to pay for. Ultimately, all companies are valued based on the expectation of future profits, and other metrics, such as MAU, DAU, growth rate, etc. are really indicators that analysts and investors use to try and extrapolate what those future profits will be.
From there, you need to execute, execute, execute. You should be executing against your own plan and your own measure of success. If you do that successfully for a few months and have a good vision and demonstrated traction then you can go share your story with investors. Your last consideration in launching your business should be how it will look to potential investors; you should NOT be executing to merely get funded by a VC, you should be working to build a viable and self sustaining business in the long run. Far too many entrepreneurs brainwash themselves into thinking that "getting funded" is the ultimate goal -- and make "short term smart, long term stupid" decisions because of that thinking.
Finding investors to fund your company is like finding a marriage partner. You'll likely have to pitch to a lot of folks before you find the one that a) understands your vision b) believes you are the right person to execute over the long term and c) agrees with you on the valuation and terms that you are raising money at. If you have a compelling business model and demonstrated traction it makes parts a) and b) easier in your pitch with potential investors.
If you have more questions or want to discuss your specific situation, I'd happy to chat more about this over the phone. Please request a call below.