Long answer: Blogging. Seriously. Write about interesting topics related to your startup. Start to pique people's interest in your product. That's where the best (and free) traffic comes from.
From an SEO perspective, does the generation of fresh content increase your rankings in SERPs by itself? Or is the idea to generate interesting content that others will link to?
It's also worth mentioning that blogging gives you a great way to go after the long tail.
I tried to reach several bloggers, most of them don't respond. I'm having a hard time finding the good blogg(ers) that would write about my app. Maybe I suck at marketing...
When pitching anyone else, always ask yourself: What's in it for them to write about me? Why should they care? Why should their readers care? How can this pitch be made into a blog post? What story do I want them to tell?
If you can answer that, briefly, in your pitch, you'll have a much easier time pitching people with success. The "My product is awesome. Here are the features. Write about me." approach rarely works.
"I want to change how you X. I do so with Y. You can do it at my service, Z." I'm not amazing at it, but if you want to trade an email or two, I'll glady trade what I leaned doing SEO work with you.
Long answer: Blogging. Seriously. Write about interesting topics related to your startup. Start to pique people's interest in your product. That's where the best (and free) traffic comes from.