I built an app for sharing useful advice/tips/perspective (like a cross between wikihow and instagram), now I need to beef up the content and user base. Is it easy/possible to piggyback off current users' email contact lists or Facebook friends, etc?
Can I rely on networking and word-of-mouth, or will I need to raise money for a marketing budget?
First of all, I guess you already know the curve of adoption is a drastically declining one.
What I mean by this: In a X-Y axis system, with the Y representing how much your users like your product and X representing how many users you have, the curve you get is a declining one.
So, at first, you have your mother, sister and friends who are super-excited about what you are building. They congratulate you even though they may not fully understand what it's all about. But hey, you are their son/brother/friend so they want to support you right?
So, in that case, imagine lots of dots high in the Y axis as your X is close to 0 - very few users. As you start growing and you targeting more users, the Y value drops, since people who don't know you and more especially don't know your product, don't give a sh@t about it. So, the picture you get is much lower Y value (user interest), which can even fall to negative values, as you move more towards bigger X values (more users, who of course you don't know).
This as an introduction to relying to friends and family. Social networks just don't scale that way. So, of course you can't rely on friends and family for scaling. You can get feedback from them, though (filter it).
What your are describing as your problem is the infamous chicken and egg problem, which is the No.1 problem a social network, a marketplace or any other platform (a website which has two user roles - producer and consumer) faces.
Now, using users' email contact lists or urging them to send out invites is a passe way for social networks to grow. Facebook, Twitter and Bebo used this method (in the old days), allowing newcoming users to leverage their email lists and invite friends to the network.
In that model, connections were the No.1 factor of importance. If a user had enough contacts, he would most probably engage with the social network. If you search for some growth hacking techniques used (and in part still being used) by Facebook and Linkedin, their aim is for a newcoming user to have a specific amount of connections (or friends) in the first X days or weeks after the signup. Because, if he fails to find friends, he will most probably abandon the social network.
Now, new social networks and platforms which have found success do not use this method. Things just got too noisy and users got fatigue from new networks urging them to invite their email lists.
What the focus now is for networks like Youtube, Quora, Pinterest, Dribble and others, is content creation before connecting users.
What this means is that you can allow your users to start creating content (which adds value to your platform) before you actually start building the network itsself.
Today’s social startups don’t start off as networks. They start off as standalone apps. They allow users to create content first. A video on Youtube, a photo with filters on Instagram, a question answered on Quora. Connections and the creation of the social network itsself is a consensequence of sharing the content and comes as a natural need for interactions between users.
Instagram started with a complete focus on one thing:
creating content (photos) and connections only came after that and as a result of sharing.
Closing, because you mentioned piggybacking and fudning.
Piggybacking is one of the techniques that has been used from some of the most successful platform startups you know. Instagram, PayPal and AirBnB piggybacked other networks to grow.
The key here is that you focus on (most preferably in a legitimate way) piggybacking the network of your focus, for example you mentioned Instagram. What you try to do here is to add value to the network, a value that is missing (tips?advice?perspective?).
APIs are your friends in this case (I assume you have a tech background or at least someone in your team has).
Now, fundraising for marketing: This depends on lots of things. Your location, your target market (international, local?), your current connections etc. If you have already built your product (your app as you said), it's not that wise to raise funds just for marketing. And it's better off if you don't rely on marketing to get users or at least do as low marketing as possible.
That's it for now.
If you have any further questions, you may contact me. Virality, network effects and further facts on social networks can be some of the topics we can discuss.