Using Tweets as a Random seed I would like to start by saying I know nothing about Cryptography and was reading up on how to choose a random seed and this link is something that I found. What I basically understood that the seed has to be sufficiently random that guessing the seed would be hard.

So the question is would the hash of a Tweet, at any given time, be a good candidate for a random seed? This is mainly because the content of a Tweet can be practically anything as it's being generated by a huge percentage of the world population.

That said, I understand it is possible to game it by mass tweeting a specific string continuously from multiple accounts flooding the tweet stream with predictable seeds. So if this can be mitigated by blacklisting the bad usernames, is using tweets for seeds a viable option?
The other answers provide very good lists of reasons not to use Twitter as an entropy source.  What follows is the flip side of your question:-

Why would you want to?

Tweets are typically read on tablets, PCs and phones. All of those have access to hardware entropy sources that can produce oodles of truly random bits for seeding anything. The zeitgeist is that you aim for 128 or 256 bits of entropy and then seed a cryptographically secure pseudo random number generator. That will meet all of your common random number needs.  

You have seeding sources such as:-


The RdRand instruction built into  most modern CPUs.
/dev/*random as part of the various favours of *nix.
Microsoft's Cryptography API. 
The cameras built into phones and tablets.  


There's not a lot of merit in pursuing Tweety entropy, other than for academic purposes.