@Christian Marin - I feel your pain! I've been at this for about 6 months now, and I have just recently started getting some deals. The best advice that I can give you is to never give up, and keep trying. You'll learn from your mistakes and get better results each time.
Here are some of the mistakes I made:
Mailpiece - A poorly designed mailpiece will greatly reduce your odds of getting a phone call that will lead to a deal. This is a numbers game, the whole goal is to get the phone ringing! I use postcardmania.com for all of my mailings, and they'll design a postcard for you for $100. So test different postcards, $100 is relatively inexpensive if you consider the ROI that it might produce through more leads. A call to action, local phone number, and listing ways that you can truly help people are important to list. If you help people get what they want, you'll always get what you want.
I've tried letters in envelopes with real stamps and labels, I've tried hand written yellow letters, (I've even tried bandit signs!) but postcards just seem to work the best for me, since that's where my deals have come from. I suggest trying them all, rotating each method throughout your list mailings, and then measure what seems to work the best for you.
Your list - I get my lists from Listsource. You can play with the criteria here, but I've stuck with older residents with equity that have a last sale date of at least 10 years. I've tried different things here, and I'll continue to adjust. Keep tweaking until you find the formula that works better. I've mailed to absentee and owner occupant, and my deals have come from both.
Your frequency - You will get deals off of your first mailing, but I've read in a few places and heard on podcasts that more deals will come from consistent subsequent mailings to the same list.
Quantity - Send out as many mailers as you can, consistently for 12 months. I started with 3000, no deals. Then 4000, still no deals. Then I sent out 8000, and I got deals! The quantity needed to close a deal will vary from market to market. Fortunately or unfortunately, I live in one of the hottest markets in the US.
The most important lesson I've learned so far is which areas to target. You need to know where the majority of the investor transactions are taking place. I mailed to where I wanted to find houses (nice appreciating areas close to my house) but I completely ignored the areas where OTHER investors preferred to invest. I'm the rookie, remember? Talk to other investors that are actually buying houses from wholesalers, and find out what areas they want to buy deals from. You might like the $150k ARV houses in the suburbs, while most of the investors are looking for $60k ARV houses in urban parts of town.
I wish you the best of luck, and please just stick with it and don't give up! YOU WILL CLOSE A DEAL!