It might take a long time to find appropriate reviewers. Therefore, waiting for an answer longer than expected is not very extreme. Quoting this answer,
Depending on the scope of submitted paper, editors sometimes have hard time to find a suitable reviewer. During the process, a considerable amount of time might be needed.
The reviewing process starts when editors send the paper to the first suitable reviewer, and ends when final review is complete. Usually, it is not a single reviewer, but several reviewers.
Unfortunately, some reviewers might reject to review the paper for various reasons
Q: How can I decide whether my suspicion is correct? What handling times should I expect?
A: There is no certain way to decide whether such suspicion is correct or not without contacting the editorial board. Expected times might be stated in the journal's web site, however stated durations might vary.
Q: Given some expected handling times, when should I act? How much leeway should I give?
A: It is natural to act if a considerable amount of time passes after the expected response time (ERT). But please keep in mind that again, this depends on the amount of ERT. For instance, if ERT is 3 months, it is not preferrable to send an email about the status in 100th day. Waiting for about twice the ERT might be a good measure.
Q: How should I act? Whom should I contact and what should I (roughly) write?
A: Only office to contact is editorial board. Writing an email to the editorial board, addressing your issues and asking for the status of your paper would be sufficient. However, if you need an immediate feedback because of various reasons, that should be stated in the mail. As an example:
Dear Dr. [Name Surname], I have submitted the paper entitled [title of the paper] to [journal name] on [date of submission]. As stated in your website, the expected response time is [duration]. Since it is passed [duration] months after the expected response time, I would like to ask the status of my paper, which is currently under review. Please note that I have a time restriction for getting an official review. Therefore, I may suggest experts of the field to help the process, if you are still seeking reviewers. Otherwise, please update the expected response time so that I can plan ahead.
If you have no time restrictions, you may simply write the same mail without mentioning the time restrictions.
