My background is in online marketing.

i find it a lot more efficient to pre-screen online and then have the conversation if everything seems ok upfront.   

Once you have an address of a property that appears to be in distress, you can go to the county assessor to find the owner (even online in some counties) for free (if you don't value your time), or you can use a paid service that will give you all the details right on your phone while you are standing out front, owner or non-owner occupied, value, comps, equity, vacant, even their phone number.

I've been on BiggerPockets a few weeks now and its safe to say this is the best networking platform for investment real estate!

A lot of information can be found online, through books, your local real estate commission, other agents, investors, etc.Focus on learning and making connections. 

Google online see what you can find.

Where are platforms to advertise other then craiglists, for serious buyers?

Go to as many as you can and meet as many people as you can.Keep your connections and reading going here on BP, your networking will be a mix of online and local if you are smart.

Cozy is great as you bring more units online and want to utilize their listing/credit and background checks/ payments.

Quick question as online info has left me confused.