Website, Blog and Twitter... is marketing yourself this way effective?

Hello, I am a Design for Interactive Media Graduate and Postgraduate Computer Science individual who... has no idea what he really wants to do.. and is struggling to find opportunities to find out due to no real portfolio or experience.

I wasn't a heavy fan of coding due to the stress of a condensed computer science masters however I understand it better now especially from this website, and my graphics design skills are mediocre. However I am attempting to build Front-End developer skills... and I am interested in digital marketing, SEO and well just general web authoring as potential careers too.

My main question is, is ploughing the hours into things like blogs and twitter actually worthwhile to employers for someone who has nothing to really show yet?

I'm stuck in retail at the moment. I would like to move on to an interactive media job of some kind.

I have sort of an action plan on paper it pretty much revolves around:

1) Development of a Portfolio website (and fill it, however I am only learning like others here so this might be awhile.)

2) so in the mean time, I build up an online presence with making extensive use of twitter.

3) Developing a "learning blog" where I write down what I learn as I go? show bits of what I've done, links to any research or other interesting topics?

Now the obvious way is to get solid HTML/CSS/JAVA skills I know. but for the SEO/Marketing/Authoring jobs ... is ploughing potentially 100s of hours into writing a blog that potentially will only be viewed by a few worth it?

Any other advice for people in my situation? I am not focused on one role, I just want to make the jump and go from there.

I'm already 26 years old, I'm fearing that awful "you should have a focus by your 30s. Employers start to ignore you in favour or fresh graduates".. I guess I'm summing this whole post up to...

TLDR: Is all this online presence (blog, twitter, linkedIN, Portfolio ect) really that attractive to employers? or a wasted distraction from learning the nitty gritty of the languages?

Thanks