I have been doing Articles submission for my websites, but there is no approciable increase in traffic and ranking of the sites. DOes articles submission really help for site promotion?

i think so
it is better to have than nothing
you can get many backlinks to your website

I must say article submission is a good source of backlinks and traffic, but kinda short-term. BLs from article submission usually disappear in Google index after a period of time.

again it will depend on the quality of your content.

If your content is meaningful and informative your will get plenty of back links and real visitor from it.

submit your article in the top 20 to 25 article directories.
if your content is appealing then it will be syndicated by others and you will get back links and real visitors.

I would like to tell one thing
concentrate on the content ..rather then submission if your content is good then you will get the popularity by itself.

With each article submission you get to create a link back to your website if done properly. What you write must be relevant to what you are promoting and choosing keywords that are relevant to your product or service

Article submission could take traffic and backlinks to you,maybe the article sites are not famous which you were submission,or you have not add several links in it?

First of all you should write really interesting articles, so other people would like to distribute it. The power of article submission is not in posting in 10-20 websites. The real power is when people post it on their blogs and sites by their will, because they like the content.

I think Article submission helps. If you are submitting many press releases with unique and valuable content with keywords to your site then google should index those pages and your ranking will go up.

Yes Article With Unique content & hyperlinks on keyword will soon boost you traffic So Use matched keyword also when writing article & hyperlink keyword when submitting

Purpose of article submission is not about traffic... it's about quality backlinks..