I submitted articles to some journals but I still do not know the fate of those manuscripts. I have written to the editors but dis not get any responses. Should I assume my articles were rejected and submit to other journals
How long it's been your submission? If it is more then 4 - 6 month and still you didn't get a single response (even to mention that they have receive the article) from the journal then it is better for you to make a move to other journal publisher.
I understand well your problem. It is often the case that a first editorial decision takes more than 4 - 6 months after the initial submission. Have you got any response acknowledging the reception of the manuscript? It is a bit strange if this was not yet case. If I were you, I would inform the Editor-in-Chief of that fact and explain to him/her that if s/he did not give you any answer within 15 days, you are going to submit your manuscript(s) to another Journal. After this deadline, you may submit your manuscript(s) to a different Journal. So, you cannot be accused of submitting at the same time your manuscript to more than one Journal.
There is always a good chance that the Editor has not been able to find enough reviewer. You may be able to track your submission on the journal website. Good luck!
If you have received acknowledgement of receipt, your manuscript is provably under the review process. It is often the case that it is difficult to find available reviwers. Do not have a system to know of the editorial status of your manuscript, saying, for example, under review? If this is the case, I would advise you to do what Isuggested in my previous answer.