Ask HN: How to do Guerilla Marketing?

I am building an application for young professionals within the Financial Industry whether they are in Ops, IT, Finance, Marketing, Sales, Investment Banking, etc...

The users I am trying to acquire must be from the same 3 companies (ex: JP Morgan Chase, UBS, etc.. ). Very targeted, ultimately, having several users from each company.

Currently I activated Facebook Ads.

1. LinkedIn Groups (Intern Class 2012, etc... ) = No, Private Groups 2. WallStreetOasis = Yes 3, Twitter Blast = No, might be conceived as spam

What are other channels I can get in-front of these users?

Thanks.