An invitation from a not-so-famous journal called "world biomedical frontiers" to feature my paper on their website I received an email from world biomedical frontiers journal:


  Your recent paper “XXXXXX” (published in “YYYYYY”) has been selected to be featured in our next issue of World Biomedical Frontiers, because of its innovation and potential for significant impact. 
  Research results with significant potential to improve health – or to treat or prevent disease – often deserve an immediate leap onto the “front page”. However, scientific breakthroughs don't always make the front page – and some don't make any page! We are the platform for you to stand out from among ~100,000 papers published each month, in order to attract more attention from the public and potential investors.
  World Biomedical Frontiers [ISSN: 2328-0166] focuses on cutting-edge biomedical research from around the globe. Our website receives more than 8,000 visits per month from an international audience of academic and industrial researchers and developers, providing greater opportunity for your results to be recognized and appreciated.
  If you accept our invitation to feature your paper on our website, a $38 processing fee will be charged. We will then post the abstract/summary of your paper in the latest section of Stem cells , with additional information from you highly recommended to further explain your novel findings and concepts in plain language; photos and/or figures are welcomed. Here are two examples (1 and 2 ).
  In order to report breaking publications in a timely fashion, please contact us within two weeks if you wish your paper to be featured in our next issue.
  Sincerely,
  
  Editor
  
  World Biomedical Frontiers,
  
  New York, USA
  
  Phone: 1-(917) 426-1571
  
  E-mails: editors@biomedfrontiers.org
  
  Website: http://biomedfrontiers.org/


Should I trust them? 

I read this question and also this one, but I wanted to know about this specific case and what to do about it.
No; this isn't how reputable venues approach authors. This will have at best zero value (possibly negative value if someone notices, which is unlikely given how little visibility they apparently have), and will cost you $38. 

(Its funny that they advertise that they get 8000 website hits per month. This strikes me as an exceedingly low count, given that they probably get a hit from many people they send this spam email to)