I am an entrepreneur who does not like to be in the limelight. Am not a big tweeter or public figure. How can I still build my cred?
Interview fellow experts. Do google hangouts with them. Audio calls. Post these in forums to get engagement. A thread with 20 replies and 250 views has a ton more credibility than a lonely blog post on your site. You are who you hang around. (Get 4 or 5 of these together and you can sell them as an information product!)
Get on radio and podcast interviews. Market these. They position you as the expert.
Publish a Kindle and/or Createspace book. This doesn't have to be lengthy; just answer a specific question in your field. Again, positioning. It's there...even if few people buy it. You can market it in your LinkedIn profile, your site, etc. and it boosts credibility just by being there.