1) Go hunting, 2) discover what is available based on your other decision criteria (e.g., core values, family, geography, career goals, economics, lifestyle), 3) after gathering information, leverage that information for the best deal. If you plan on weighing your decision between leaving and staying then have a respectful discussion with your employer about your values and long-term goals. If they get angry or offended that you are looking after your best interests then know that this is unreasonable (i.e., THEY need to grow up) and probably a sign that you are in an abusive one-sided employment relationship. If they are smart and value your contribution then they will work to retain you. Retention is MUCH less costly than recruitment of talent.
IF you approach your employer prior to the discovery process then you will not be armed with the information you need to make the decision. It is important to have a very clear idea of both your and your employer's best alternative to a negotiated agreement (or BATNA). Attack their BATNA while strengthening your BATNA. Distinguish between your core INTERESTS in making your decisions (which are not any of your employer's business) and your POSITION that you take as you negotiate.
This isn't a marriage. This is a transactional relationship. Don't be a sucker. They will use every tool, including your misguided sense of loyalty, to extract maximal value while minimizing your compensation. That's the game. Have fun.