The short answer is you make new associates online in the same manner you do in the real world. You start by finding out about one another and determine if there is a reason to continue to do so. Its a lot like rocket science without all the rocket or any of the science.
The long answer is oddly enough, longer. You start by finding someone and viewing their profile. Obviously some profiles are filled out extremely well and others aren’t. Glean what you can from what is written. Don’t make the assumption that because their profile isn’t properly filled out that they aren’t worth knowing. Lots of great and busy people get online and are still waiting for “later” to come so they can fill out their profile.
If you see something you like, send them a note that says-
“I came across your profile on x platform and I really like what you wrote about X.” (Copy their sentence and paste it right into your note). Tell them why that sentiment resonates with you and suggest a way to follow up via either phone or email.
Lots of people try to set up face to face meetings through linkedin or other sites. Color me old fashioned, but I think a first meeting, if not at an event, should be over the phone. This gives you a chance to explore the synergies and then determine if a face to face is in order. The reality is everybody is busy. There is no sense in meeting with a lot of people under the guise of “networking” if we will only be “netting” together.