WhatsApp was founded by Jan Koum and Brian Acton.WhatsApp joined Facebook in 2014, but continues to operate as a separate app with a laser focus on building a messaging service that works fast and reliably anywhere in the world.WhatsApp started as an alternative to SMS. Whatsapp now supports sending and receiving a variety of media including text, photos, videos, documents, and location, as well as voice calls. Whatsapp messages and calls are secured with end-to-end encryption, meaning that no third party including WhatsApp can read or listen to them. Whatsapp has a customer base of 1 billion people in over 180 countries. It is used to send personalised promotional messages to individual customers. It has plenty of advantages over SMS that includes ability to track how Message Broadcast Performs using blue tick option in Whatsapp. It allows sending messages to Do Not Disturb(DND) customers. Whatsapp is also used to send a series of bulk messages to their targeted customers using broadcast option. Companies started using this to a large extent because it is a cost effective promotional option and quick to spread a message. Still, Whatsapp doesn't allow businesses to place ads in their app.
SEM is the wider discipline that incorporates SEO. SEM includes both paid search results (using tools like Google Adwords or Bing Ads, formerly known as Microsoft adCenter) and organic search results (SEO). SEM uses paid advertising with AdWords or Bing Ads, pay per click (particularly beneficial for local providers as it enables potential consumers to contact a company directly with one click), article submissions, advertising and making sure SEO has been done. A keyword analysis is performed for both SEO and SEM, but not necessarily at the same time. SEM and SEO both need to be monitored and updated frequently to reflect evolving best practices.
However, if you are seasoned online marketer, and you've built a substantial following, then marketing as an affiliate might be the right fit. Jason Stone from Millionaire Mentor has built a seven-figure business with affiliate marketing, while David Sharpe from Legendary Marketer has built up an eight-figure business by creating an army of affiliates that market products in collaboration with his team.
Facebook pages are far more detailed than Twitter accounts. They allow a product to provide videos, photos, longer descriptions, and testimonials where followers can comment on the product pages for others to see. Facebook can link back to the product's Twitter page, as well as send out event reminders. As of May 2015, 93% of businesses marketers use Facebook to promote their brand. A study from 2011 attributed 84% of "engagement" or clicks and likes that link back to Facebook advertising. By 2014, Facebook had restricted the content published from business and brand pages. Adjustments in Facebook algorithms have reduced the audience for non-paying business pages (that have at least 500,000 "Likes") from 16% in 2012 down to 2% in February 2014. 
Digital marketing is defined by the use of numerous digital tactics and channels to connect with customers where they spend much of their time: online. From the website itself to a business's online branding assets -- digital advertising, email marketing, online brochures, and beyond -- there's a spectrum of tactics that fall under the umbrella of "digital marketing."