Assuming the startup has a product, your questions should center on impact and growth.
1. Impact: What problem are they solving for users? How are users using the product?
2. Growth: How quickly are they growing users, both free and paying? How are they acquiring users?
If the startup has a convincing answer for 1, they're working on something concrete. If they don't have convincing answer, probe deeper to find out if they have tangible plans for what they're going to create.
If they answer question 1 well, ask them 2. If they're growing users quickly (for instance, double digit % week over week), the startup is totally worth considering. If they're not growing quickly, ask them how they plan to grow. It's useful to know how they're acquiring users -- if they're spending money to get users, you should ask if it's scalable. If they're getting users without spending much money, great.
Growth can fix most problems in a startup -- it attracts users, investors and talent. If they aren't seeing growth, they should at least have a tangible impact with the users they have and plans for growth.
Double digit week over week week is only possible for very early stage startups. 10% week over week for a year is 142x yearly, which just isn't sustainable for more than a year or two at the absolute maximum.
1. Impact: What problem are they solving for users? How are users using the product?
2. Growth: How quickly are they growing users, both free and paying? How are they acquiring users?
If the startup has a convincing answer for 1, they're working on something concrete. If they don't have convincing answer, probe deeper to find out if they have tangible plans for what they're going to create.
If they answer question 1 well, ask them 2. If they're growing users quickly (for instance, double digit % week over week), the startup is totally worth considering. If they're not growing quickly, ask them how they plan to grow. It's useful to know how they're acquiring users -- if they're spending money to get users, you should ask if it's scalable. If they're getting users without spending much money, great.
Growth can fix most problems in a startup -- it attracts users, investors and talent. If they aren't seeing growth, they should at least have a tangible impact with the users they have and plans for growth.