How will you measure ROI (return on Investment) for new start up company looking to invest on Social media campaign?

I would suggest that you go for google adwords rather than facebook.. if it's linked in then i guess it's ok. there are a lot of experiment conducted how effective facebook campains are and if you base it on the interaction of the audience who like your page then it would be just the same as the audience you get if you purchase "like farm" outside of facebook.

Anticipated ROI

Anticipated ROI = (Anticipated Revenue from SEO efforts – Proposed Cost of the SEO Project)/Proposed cost of the SEO project

Actual ROI

Actual ROI is the one which eventually decides the fate of your future engagement with a client.

Actual ROI= (Total E-Commerce Revenue through SEO + Total Goal Value through SEO) –

cost of running the SEO campaign/ cost of running the SEO campaign

Read more: http://www.optimizesmart.com/roi-calculations-seo/#ixzz3h4F0PtU3