Generally, you cannot force search engine to index your site in any way. Submitting sitemap only gives a hint that a page exists, however because of extremally large number of spam pages, the external links are what matters the most.
When you have your own blog, which is itself indexed, it's a great idea to write short article about your site and add a link. Blogs created on wordpress.com etc. are indexed quite fast (however, sometimes you must wait a few days/weeks before it gets indexed fully and can be used to promote other sites).
Note that posting links on such pages like that will not help your site to be indexed, because of rel="nofollow" which is automatically added ;)
