How useful are online job portals to job seekers these days?

It depends on the features provided by the job portal but generally speaking it's more effective than other means of job search.
It maximizes their chances of finding jobs by keeping their options open.

I totally agree with Abrar, Through Bayt.com the job seeker will be able to check all the current openings and apply for those vacancies that match his/her current qualifications.
This would take place by Job Search Tools (Title, industry, company ...etc), Job Alert Services according to the resume posted on website , Job Application History and Interview/Walk-in Alerts (My Workspace), 247 availability of service, Multiple Resumes service, targeting multiple opportunities (creating more than one Cv that suit more than open vacancy from the same workspace and using the same username and password), Help and Guidance through consultants

Very useful if you're intelligent enough to use them to their full potential.
Someone who creates a comprehensive profile, keeps it updated, visits the job portal atleast once a day and applies for relevant jobs; has a great chance of landing an interview.

There is still no substitute for a leading dedicated career portal for staying abreast of the job market, managing one's career and maximizing one's chances of landing that next job.
Essential for maximizing success however is to understand what exactly one is searching for and to find a leading regional jobsite that very specifically caters to the same.
Jobseekers maybe well advised to look for a leading jobsite that among other things - 1.
Has proved its mettle as the fastest, easiest and most effective way for employers to find top talent and jobseekers to find top jobs in the region (eg Bayt.com successfully serving MENA since 2000)).
2.
Has built vast regional inroads and has regional dedication, understanding, expertise and success 3.
Has maximum choice in terms of top employers and top jobs as more choice translates into more opportunity (Bayt.com the leading MENA jobsite has over 11 Million registered professionals today - which means more employers post more jobs) 4.
Has constantly updated, industry-leading, state-of-the-at tools and technologies that allow sophisticated Search and filtration as well as real-time tracking of CV performance and success metrics 5.
Has a robust brand (look for brand dynamism and vitality) 6.
Has great testimonials (from both employers and jobseekers) 7.
Has rich career management tools (eg.
Bayt.com's Career Map, Bayt.com Blog, Bayt.com Industry Research, Bayt.com Career Articles and Guides) 8.
Has an active and leading and constant presence in media and awards and career events and thought leadership events across the region.
9.
Is ahead of industry trends (Look for constant innovations eg.
Bayt.com Specialties, Bayt.com Workspace, Bayt.com Career Map, Bayt.com Career Digest) 10.
Has a brand you LOVE and that loves you right back! Brand affinity always adds that extra touch of spark.
Good Luck!!!!

That's right Abrar, the more job seekers have tools & features the more they will benefit from job portals.
Advanced technology makes job seekers more engaged to the job portals, i also believe that the number of active/fresh job posts play key role in attracting new visitors to the job portal and make them hunt their relevant jobs!

Rana, You are talking about empowerment, and that's what job seekers gain from using their profile in Bayt.com, they have wide choice in choosing their dream job by the technology & facilities in their account.
Thank you for your answer.