Independent publishing of paper resulting from a project
You should definitely contact your former supervisor. If you do not have his contact information yourself, then you could try asking colleagues at your institution - such as a professor in the same research group.

While authorship norms do vary by field, the supervisor's contribution (having the original idea, defining the project, helping you in general) is surely enough that he should at least be asked. My impression is that even in those fields where supervisors might not be authors, it would still be very bad to try to publish a paper without talking to the supervisor about it. For all you know, he is planning to publish, and would be justifiably angry if you pre-emptively submitted your own version - and even had it accepted. Even if did not expect to be a co-author, he may still be upset if he does not have the chance to help make the paper the best it could be.1

If the supervisor would like to be a co-author, then he should certainly be able to help with venue selection, and adapting the document from a thesis to a paper. Generally, it's not just a matter of changing the formatting - each kind of document has its own requirements, which aren't exactly the same. For example, in a dissertation you will probably spend more time on general background material than in a paper. The work you have done might not be substantive or original enough for all journals. Receiving advice at an early stage may well make a huge difference in the quality of the submitted paper. (You can still seek advice from others, if the original supervisor can't help.)

As far as whether you should submit a paper at all: I think you are thinking along the correct lines. It may help your career - it certainly shouldn't harm it - and you will be contributing to the general advancement of human knowledge. On the other hand, it will take some amount of work. Again, someone who is more familiar with your research area can take a look at your thesis and give advice about just how much work that might be.

1. Example: A colleague of mine is a mathematician. His student submitted a paper, based on the student's own work. The professor did not expect to be an author, especially since he didn't contribute to the mathematical content. But he was upset that the student hadn't asked him for advice about preparing and submitting the paper. He was also embarrassed that he found out about the paper's existence from a third party.