SEM only

Hello. I'm wondering if social media is part of SEM. If yes, it means that SEM is proven to be effective to promote your business even without doing SEO. I'm seeing that most companies rely only on social media promotions nowadays. Do you think it's ok not to do SEO anymore? Thanks.

 

Wikipedia: Search engine marketing

Search engine marketing (SEM) is a form of Internet marketing that involves the promotion of websites by increasing their visibility in search engine results pages (SERPs) primarily through paid advertising. SEM may incorporate search engine optimization (SEO), which adjusts or rewrites website content and site architecture to achieve a higher ranking in search engine results pages to enhance pay per click (PPC) listings.
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Yes, I read that before posting this thread but I was wondering why some people just settle for SEM. I was asking because I'm about to hire an agency for their digital marketing services and I was thinking of going for both SEM and SEO. It'll probably be more expensive but more effective.

 

Probably so.