We've talked about how having a socialisation quota can help introverts in networking better. If you who have trouble keeping up with current contacts, booking a weekly "social hour" might help.
Scheduling time can help achieve that task, author Paul Sanders advises:
When you make that decision, you won't have to remember to call people, you'll just do it for one hour and enjoy the week without worrying that maybe you're ignoring people.
During that hour, contact new and old friends, and try and make plans to meet with some of them. If you have one social activity per week, that's far better than having no clarity and no consistency.
Sanders also suggests introducing your friends to each other, so you can meet larger groups in one go. And eventually, they might call each other and make plans, inviting you along.
How An Introvert Can Build A Great Social Life [Change Your Thoughts Change Your Life]